All about computers

What is the computer?

A computer is an electronic device, designed and operated under the control of stored programmed instructions. Through the use of
hardware, it accepts data, processes that data and stores the results for future use or outputs it in a meaningful form for the user. The
way the computer works is illustrated in the flow chart below (Fig. 2.1):

Fig 2.1. Showing a simple diagrammatic representation of the flow of data in the
computer.
Data versus Information
These two words, though often used interchangeably in everyday life, have meanings that are separate from each other in the
information technology world. Data refers to a collection of raw, unprocessed or unorganised facts and it may include text, numbers,
graphics, images, sounds or videos.
Information refers to processed and organised facts that have meaning and purpose.
Computer Hardware ... What is it?
Computer hardware is the equipment that makes up the complete system. It is inclusive of the electrical and mechanical components
such as the keyboard, the monitor, the systems unit and its constituents and all other externally connected devices such as the printer or
scanner.
The equipment or devices that make up computer hardware may be broken down into categories relating to the role they play in the
data processing cycle. These categories are illustrated in the chart below (Fig. 2.2):

Fig 2.2 Showing categories of devices in computer hardware.

Isolating the Systems Unit
The systems unit is the most central of all computer hardware. All other hardware is attached to the systems unit. It is the home of the
central processing system (CPU) and, by extension, the site where all processing takes place.
The Central Processing Unit (CPU)
The central processing unit, or CPU, is the heart of the computer, which is responsible for the processing of data entered into the
computer, so information to be stored or outputted may be produced. The task of the CPU is a mammoth one! That is why it has sub-
units such as the control unit, Arithmetic and Logic Unit (ALU) and registers that help it in achieving its purpose.
 Control Unit (CU): The control unit is the part of the CPU responsible for the fetching and executing (carrying out) of the
programmed instructions used to operate the computer. It generally controls the transfer of data to and from the CPU. It can also
send a command for data to be transferred from the main memory to the printer. Hence, the CU, by sending information to
different devices in the system, controls the flow of data in the computer.

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  Arithmetic and Logic Unit (ALU): It is a major part of the CPU and receives all instructions containing arithmetic which involves
checking the value of an item of data. It deals with the processing of these items of data. The ALU is also responsible in instances
where logic, drawing comparisons between items of data, is required. It has a set of internal locations for storing data for
immediate operation.
 Registers: a set of special internal storage locations, found within the ALU, and are responsible for storing data for immediate
operation.
Categories of computers

Categories of Computers
The influence of computers on our daily activities is grand and far reaching, thanks to the various types and forms of computers
available. With this obvious fact, persons studying these devices have developed categories to make their study easier.
They have been classified into categories based on the structural design or architecture, the speed at which the instructions are
executed, the amount of memory, the capacity of the external storage devices, and the speed of output devices and the number of
users.
Based on structural design, computes are categorised as follows:
 Microcomputers/personal computers
 Mainframe computers
 Minicomputers
 Super computers
Microcomputers
Microcomputers are small-scaled computers, usually designed for use by a single user. It generally carries only one processor and an
instruction length of 32 bits. Memory capacity of as many as two gigabytes (i.e. 2 x 109 bytes) and fixed storage capacity of 500
megabytes (or 500 x 106 bytes ) to several gigabytes. These computers are used at schools, homes, small and medium businesses.
Example of microcomputers:
 Desktop computers
 Notebook computers
 Laptop computers
 Palmtops
 Personal digital assistants
Mainframe Computers
These are huge and expensive computers with great processing power and at least one gigabyte of memory. It can be used by many
people at the same time and to carry out large tasks.They are used in hospitals, banks, government agencies, commercial and industrial
users. There is always a special team to manage its operation.
Minicomputers
Minicomputers, as the name suggests, are 'mini' versions of the mainframe computers. They are very similar to the mainframe computer
in that they can run the same type of applications as mainframe, however, they lack the speed and storage capacity characteristic of a
mainframe computer. They can support several users, as many as a few thousand connected computes. A memory size of several
gigabytes, instruction length up to 64 bits and a storage capacity of several terabytes makes minicomputers perfect for use in medium
sized business.
Super Computers
These are usually extremely large mainframe computers, capable of storing large amounts of data, instructions and information. They
are designed for application in special areas, such as performing scientific simulations nuclear energy research, medical research,
meteorology, structural analysis and geological data, just to name a few.

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Factors Influencing a Computer's Power
There are several factors affecting the power of the computer that one must consider when one attempts to choose a computer to
perform a given task or function. Some of these factors are:
 The speed
 The accuracy
 The storage capacity
 Its reliability and consistency
We have come to the end of this week's lesson. Next week, we'll be learning about the primary storage devices and media. Until then,
keep up the good work and remember, work not hard but very smart.
Fundamentals of hardware and software

The computer system

A computer may be defined as an electronic device which accepts input, processes the input and produce results (output), and stores
data and results for future use.
Before we look at the main components of the computer system, let us first look at the difference between the terms data and
information.
Data is a set of raw facts and figures that a computer processes by following a set of instructions called a program, while information is
the processed data.
The main components of a computer system are hardware, software and the user.
Hardware
This is the name given to the physical parts of a computer that you can see and touch. These hardware components are also called
peripherals. Peripheral devices are any external devices or components connected to the system unit such as a mouse, keyboard,
monitor, etc. The system unit is the box-like case that houses all the electronic components of the computer.

There are five general categories of hardware, namely:

Input devices
They get data into a computer. A mouse, keyboard, joystick, biometric systems and a scanner are all examples of input devices.
The central processing unit (CPU)

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This is the brain of a computer which controls how the rest of the computer works. It is assisted by the control unit (CU) and the
arithmetic logic unit (ALU). The CU carries out instructions in the software and directs the flow of data through the computer; the ALU
performs the calculations and logic operations.
Output devices
They get processed information out of a computer, for example to a printer, monitor or even speakers.
Storage devices
These include floppy drives, hard disk drives, flash drives, CD- ROM drives and so on that are used for storing information permanently.
Memory
This enables a computer to temporarily store instructions and data.
Below is a diagram which illustrates the processing cycle of a computer system.
The Data Processing Cycle

Software
This is the name given to the computer programs that tell the hardware how to work. Without software, the computer hardware would do
nothing as there would be no instructions.
Computer programs
These are instructions (programs) produced by programmers to create system and application software.
System software
This software is usually called an operating system since it controls the hardware and how all the other software works. The most
commonly used operating system is Windows, made by Microsoft Corporation.
Application software
This software instructs a computer to carry out or perform a specific task. Word Processors, Spreadsheet and databases are all
application software.
User
Any individual who interacts directly with a computer system.

Input Devices
.
Input devices are those that get data into the computer for processing. Input devices can be categorised as:
 Keyboard entry devices and touch terminals
 Pointing devices
 Source data entry devices
 Multimedia input devices
Keyboard
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The keyboard is considered to be one of the most commonly used input devices available to the user. Whenever data is entered via the
keyboard, the keyboard converts the letter(s) into a binary code (the machine language). For example, the letter 'A', when pressed, is
converted to this binary code 01000001. This code is then sent to the CPU for processing.
Types of keyboards include the QWERTY keyboard, Dvorak, Enhanced, wireless and the Braille keyboard which was designed with raised
dots to provide assistance to the blind.
Point of sale terminals (POS)
Point of sale (POS) terminals are used to read barcodes which are usually printed on commercial products. They are also used for reading
printed information by passing a wand across a special tag attached to an item, or entering relevant data via a keyboard. When an item
is scanned, the terminal displays the scanned data then prints an itemised sales receipt that shows the total amount of the purchase,
including taxes. Places you will likely see such a transaction taking place include the supermarkets, stores and so on.
Automated Teller Machines (ATM)
Automated teller machines (ATMs) accept user input in the form of transaction requests. The request could be for withdrawal, deposit or
bill payment. The request is sent to a main computer for processing and the result communicated to the user. ATMs are also now being
used to add credit to your cellphones.
Pointing devices
Mouse
The mouse is the most commonly used pointing device. The average mouse produced today comprises two buttons which the user
depresses to select items from a menu or click on graphical objects on the computer screen (icons), thus sending commands to the
computer. The position of the mouse is shown on the screen by the mouse pointer. Three main types are the mechanical mouse, the
optical mouse and the wireless mouse.
Trackball
This device resembles a mechanical mouse, except that the ball is situated on top of the mouse and is bigger in size. Movement is
provided by the user's hand or palm to control the cursor on the screen.
Joystick
The joystick is a vertical stick used to control cursor motion/movement on the screen for the playing of computer games.
The light pen
The light pen is a device that is used to input digital signals to the computer by writing directly on the screen. This is made possible by
the computer with special software to detect the presence and absence of light.
The graphic tablet or digitising pad
The graphic tablet/digitising pad is a board which detects the location of the pen-like stylus on its surface. The tablet converts drawings,
photos, and so on to digital signals. This is made possible by the pad or tablets, not the pointing device. They are used in conjunction
with a pen or stylus which is held in the hand and moved across the surface of the tablet or pad.
Touch screen
This is a screen through which data can be inputted to the computer by touching the item or picture being displayed on the screen with a
finger. Items are selected just as they would be with a mouse, pointer or a light pen. A touch screen is considered a user-friendly method
of inputting data, especially for non-specialist users. Users can select items from a menu by simply touching images of object displayed
on the screen. Touch screens are used in the following areas:
 Public information systems (PIS)
 Health-care centres
 Restaurant/point of sale terminals
 Customer self-service locations
 Computer-base training
 Automated teller machines
Source data entry devices
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Source data entry devices use special equipment to collect data at the source and send it directly to the computer, thus eliminating the
possibility of human error in data entry. Let us now look at such devices:
Magnetic ink character reader/recognition (MICR)
The MICR uses ink containing magnetic particles in order to print magnetic characters on cheques. This special type of ink is used to
record cheque particulars such as the cheque amount, account number, branch number and so on. The information on the cheque is
then scanned into a computer and stored permanently for bank purposes.
Optical character reader/recognition (OCR)
OCR uses a photoelectric device to scan characters (printed or handwritten) and convert them into electric signals to be sent to the
computer for processing, where they are converted into a text file. The billing system of an electric utility company is one such place
where this application can be utilised.
Optical mark reader (OMR)
This is a special machine that uses infrared light to scan pencil marks on pre-printed forms such as multiple-choice examination answer
sheets, questionnaires and so on.
Scanners
A scanner, which is similar to a photocopier machine, scans documents containing text or graphics as a full page and transmits the
image to the computer as a code, which enables the file to be saved as a digital file. There are different types of scanners, namely, the
flatbed scanner, the hand-held scanner and the laser scanner which is built into the POS terminal used to read the barcode on an item.
Barcode reader
Barcodes are coded light and dark lines found on products of all kinds. The barcode is used as an identifier of the product on which it is
found. A barcode reader is a scanning device with a sensitive tip which contains a light source and light detector used to read the
barcodes on an item. Barcode readers are used at supermarkets and some libraries.
Sensors
Various sensors are used to measure heat, light, sound, movement and pressure. The measurement recorded by the sensor is sent to the
CPU where it is analysed and the relevant output is given. Sensors can be used to monitor a patient with a heart condition, create
characteristics in robots that mimic human senses, etc.

Input and output devices

Multimedia input devices

The remote control
By pointing to its target and depressing one of the buttons on the button pad, the remote control emits a beam of infra-red light which
transmits data signals. Remote control is commonly used for input to TVs, VCRs and other devices, plus they are now being used by
computers as a wireless method of communication.
Digital camera
This is a type of camera that stores photographed images electronically instead of on traditional film. After the image has been captured,
it is downloaded by a cable (which is normally purchased with the camera) to the computer, using software supplied with the camera.
The user then has the opportunity to edit, delete, store, etc the photos on the computer. This is also used to store small movie clips.
Voice recognition devices
With these devices, special software is used to convert voice into text or to activate menu options. Voice recognition devices require
high-speed processing and a large memory.
Microphone
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Microphones form a part of most voice recognition systems. Microphones can capture sounds from the air which are good for sounds
effects or voices.
Biometrics (input signals from the human body)
Biometrics systems identify a person through a fingerprint, voice, retina/iris scan or other biological characteristic(s). In using the iris for
personal identification, the user's iris is scanned and a biometrics digital certificate is released, which guarantees authenticity and
identity.
Webcam
This camera is designed especially to sit on your computer. It feeds pictures directly to the computer. For example, you could sit in your
room in Jamaica and communicate using your messenger (MSN) to someone in the US and they can see you while you text or speak to
them because the camera allows for voice input and output. However, a disadvantage of this device is that you are limited by the length
of the cable that connects the camera to the computer.
An output device is a device which receives data in the form of electrical pulses from the CPU. It then converts this data into a form that
can be understood by the user, a machine or another process.
There are two main categories of output devices: soft copy output devices and hard copy output devices.
Soft copy output devices get information to a computer monitor or other temporary output device that you can see but not necessarily
touch (intangible).
Let us now look first at the visual display unit (VDU).
The Monitor/VDU/Screen
This device provides output to the user. The video display adapter on the motherboard allows information to leave the processor and
appear on the monitor. This type of copy that the monitor shows is known as soft copy, which, as stated above, is intangible.
Key terms associated with the monitor
 Resolution
This is measured based on the output quality of the screen. If the monitor displays graphics and video images accurately, then there
should be no grains, colour change or distortion. In addition, the greater the pixels per inch of the screen, the higher the resolution.
 Pixel
This is the short meaning for picture element, which refers to the dot per inch of the screen. The greater the number of pixels, the better
the quality of the image.
 Size
Monitors come in various sizes: 14 inch, 15 inch, 17 inch, 20 inch, and, with today's increased technology, they can be purchased in
larger sizes, but they would be more expensive.
 Types
The types of monitors can be derived from the technology they employ. The two most popular technologies used are cathode ray tube
(CRT) and liquid crystal display (LCD).
 Cathode ray tube (CRT) uses electron guns that must be at distances of over one foot from the screen. Three electron guns are
used to set the dots glowing to see all the different colours. CRT technology is used with computer systems that are not frequently
moved from one place to another. Examples of such computers are desktop computers, minicomputers, mainframes and super
computers.
 Liquid crystal display (LCD) is the most popular current technology for flat-screen display used for pocket calculators and digital
watches. It is even now available in television. LCD comprises liquid crystal material between two glass plates. Characters are
etched on to the inner sheet but cannot be seen.
Audio output devices
Audio output devices include those that output voice or voice-like sounds and those that output music and other sounds. These include
headphones, speakers, earphones, sound cards, etc.
Voice output devices
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Voice output devices convert digital data into speech-like sounds. Two types of voice output technology are speech coding and speech
synthesis. Voice output is used in telephone information systems (for example, checking your voicemail), banks (for example, to check
the balance on your account) and utility companies to check for bills, automobile system warning devices and weather reporting
applications.
Hard copy output devices
Hard copy output devices are those that provide output on printed paper or other permanent media that is human readable (tangible).
Examples of devices that produce hard copy are printers, plotters, and microfiche, and examples of hard copy are a flyers, letters, books,
cards and so on.
Printers
The purpose of the printer is to display, on paper, the information shown on the computer screen. The quality of what is on paper and
how fast the information is put on the paper is dependent on your choice of printer.
Characteristics of printers
" Printer speed - The speed of a printer is measured in:
 CPS = characters per minute
 LPM = lines per minute
 PPM = pages per minute
" Printer quality - This is determined by the printer's resolution, which is measured in dots per inch (dpi). This determines how smooth a
diagonal line the printer will produce. Thus, to output text or graphics (such as photos) at a high quality, the resolution would have to be
quite high.
There are two types of printers: impact printers and non-impact printers.
IMPACT PRINTERS
With this type of printer, a hammer strikes an inked ribbon on to the paper to form a character, like a typewriter.
Advantages
 Less expensive
 Can make multiple copies of a document
Disadvantages
 Noisy
 The print quality is poor
 Poor graphics or none at all
Impact printers include Dot Matrix, Daisy Wheel and 'Band' or 'Train' printer.
Types of impact printers
Dot matrix

This printer is relatively inexpensive and can print between 100 - 200 cps. Typically, a character is made up of a dot matrix 5x7. The
characters are printed one at a time. Some printers are unable to produce graphics, only letters and numbers.
Advantages
 Inexpensive
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  Can make multi-copy forms
Disadvantage
 Slow
Daisy Wheel

This printer operates at slow speeds, less than 75 cps. It is noted for letter quality and is used extensively for professional word
processing. Characters are fully formed on the 'petals', like typewriter keys. The petal strikes an inked ribbon to produce a character.
Advantage
 Best print quality
Disadvantages
 Very slow (will print between 20 to 80 cps)
 Only one font can be used at a time because you must change out the daisy wheel to change fonts.
 Cannot print graphics
Band OR 'Train' Printer

The character set is in a continuous loop of characters. Usually, the complete character set is repeated several times around the loop.
The loop rotates in a horizontal line. There is a set of hammers across the paper. The hammer for each character position strikes the
paper and a carbon on to the right character on the chain as it goes around.
Advantages
 Very fast
 It will print up to 3,000 lines per minute
Disadvantages
 Very expensive
 Very loud
NON-IMPACT PRINTERS
With this type of printer there is no actual striking of the paper. Instead, it uses ink spray or toner powder, heat and special paper.
Advantages
 Quiet
 They can print graphics and often a wider variety of fonts than impact printers
Disadvantages
 They are more expensive
 They cannot produce multiple carbon copies
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Types of non-impact printers
Ink jet

The ink jet printer in comparison to the dot matrix or daisy wheel printer has a much faster printing mechanism. Characters are formed
by spraying ink on to the paper.
Advantages
 It is quiet
 It produces high- quality text and graphics
 It is able to print colour
 It is faster than impact printers
Disadvantages
 It cannot produce multiple copies
 The ink can smear on the paper after printing is done
Thermal printer

This type of printer uses heat on chemically treated paper to form characters. A thermal printer is similar in nature to a fax machine that
uses special rolls of paper.
Advantage
 It is quiet
Disadvantages
 It is expensive and requires a special paper to print
 It cannot produce multiple copies of a document
Laser printer

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Laser printers are extremely fast and they can produce high-quality output. They can also print one page at a time. Laser printers work
like a copy machine, using toner and a heat bar.
Advantages
 Very fast (they can print from four to 16 pages per minute)
 They produce high-quality printing
 They are extremely quiet
 They can print colour
Disadvantages
 They are expensive to buy
 They cannot use multiple-copy paper
Plotters

A plotter is a special-purpose output device that is used to produce sophisticated graphs, charts, maps and three-dimensional graphics as
well as high-quality coloured documents. They can also be used to print larger size documents. There are two main categories of plotters:
vector and raster plotter.
Microfiche

The computer can output tiny images on rolls/sheets of microfilm. Microfiche is a rectangle sheet of microfilm large enough to contain a
number of pages (or frames) of data. They can store from 30 to 300 pages. One microfiche is equivalent to 200 pages of A3 paper.
Disk or tape
This is a triple-purpose media. They are used for input, storage and output. The CPU can send output directly to disks or tapes. They are
also classified as being machine-readable devices.
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We have come to the end of our lesson. See you next week. Remember, if you fail to prepare, prepare to fail.
Memory storage

The purpose of memory is to provide storage for data, instruction and the result of processing. There are four main categories of memory
storage chips are:
 Random Access Memory (RAM)
 Read-Only Memory (ROM)
 Cache
 Buffer
A memory chip is a chip that holds programs and data either temporarily or permanently.
RANDOM ACCESS MEMORY (RAM)
RAM or primary storage is the chip that is located nearest to the CPU and referred to as being volatile. RAM is considered to be volatile in
that its content is erased whenever the flow of electricity to the processor is terminated. This is why your teacher will often remind you to
save your work frequently. RAM performs three main functions:
 Stores data for processing
 Stores instructions for processing the data
 Stores processed data (information) that is waiting to be sent to an output or secondary storage device.
READ ONLY MEMORY (ROM)
A ROM chip stores data permanently or is often time referred to as being non-volatile. The information on a ROM chip is stored on it by
the manufacturers and cannot be modified or erased by the user. The processor can read and retrieve the instructions and data from the
ROM chip, but its content cannot be changed. Whenever you turn on your computer and your computer is booting up, messages are
made possible by the information in ROM.
There are several variations to ROM:
Programmable Read Only Memory (PROM)
The PROM chip is left blank by the manufacturers and written to by the customer. Once written to the chip, it becomes read-only
memory.
Erasable Programmable Read-Only Memory (EPROM)
EPROM is a reusable PROM-chip that can be erased by a special ultraviolet light. EPROM holds its content until erased and new
instructions can be written on it. To reprogram an EPROM chip, it has to be removed from the computer.
Electrically Erasable Programmable Read-Only Memory (EEPROM)
EEPROM chip is similar to an EPROM chip, except that it is erased by applying electrical pulses to the chip, making it possible to
reprogram the chip without removing it from the computer.
CACHE MEMORY
Cache memory is a special high-speed memory designed to supply the processor with the most frequently requested instructions and
data. Instructions and data located in cache memory can be accessed many times faster than instructions and data located in main
memory. The more instructions and data the processor can access directly from cache memory, the faster the computer runs as a whole.
BUFFERS
A buffer is an internal memory area used for temporary storage of data records during input or output operations. For example, most
modern printers are equipped with buffers that store information or data to be printed.
UNIT OF STORAGE
Key definitions of terms
 Bit - the smallest unit of storage in a computer, which is usually 0 or 1.
 Byte - comprised of eight bits.

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  Word - the amount of bits the computer can process in one operation.
 Word size/length - the number of bits in a word.
 Bi-stable device - a device which exists in two possible states. This device is similar to a light switch which can either be on or off.
Once you are considering to purchase a RAM chip (memory), hard drive or a flash drive, you will first likely have to consider the size or
the number of bytes the storage medium has. Let us now examine larger units of storage by the byte table shown below.

NUMBER OF BYTES
Binary Decimal
NAME Symbol Approximately Actual
Measurement Measurement
1000
Kilobyte KB 210 103 1024
(1 thousand)
1,000,000
Megabyte MB 220 106 1048576
(1 million)
1,000,000,000
Gigabyte GB 230 109 1073741824
(1 billion)
1,000,000,000,000
Terabyte TB 240 1012 1099511627776
(1 trillion)

Secondary storage media

In today's lesson, we will be looking at secondary storage media. This became necessary due to the fact that primary storage devices
such as RAM and ROM are limited in size and are temporary or volatile, while secondary storage is permanent and can be used for
backup purposes and future use. A comparison can be made among the variety of secondary storage devices in respect to their
portability, speed and capacity.
Let us look at each of these key factors
Storage capacity
This is referring to the amount of information that a particular storage medium can hold. Large-capacity storage devices are more
appreciated and preferred for many sophisticated programs and large databases.
Access speed
This refers to the average time needed to locate data on a secondary storage device. Access time is measured in milliseconds.
Portability
This refers to the ease and accessibility of a device to transfer information from one computer to another.
Every secondary storage device or medium requires its own drive. Media (singular: medium) are the physical hardware on which a
computer keeps data, instructions and information for future use. Examples are diskettes, hard disk, compact disc and tapes. Storage
devices record and retrieve data, instructions and information to and from storage media. Examples are floppy disk drive, hard disk
drive, compact disc drive.
Secondary storage devices fall into two main categories:
 Direct Access Storage Devices (DASD)

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  Serial/Sequential Access Storage Devices (SASD)
Direct Access Storage
This is where any data can be accessed without reading any other data items first (randomly). Examples: floppy diskette, flash drive,
hard disk drive, etc.
Serial Access Storage
This is where all data between the read/write head and the required data has to be passed over before the data can be accessed.
Read/Write Head
A device that reads data from and writes data on to a storage media.
Types of storage media
 Floppy diskettes
 Hard disks
 Magnetic tape
 USB flash drive
 ?CD-ROM (Compact Disc Read Only Memory)
 ?WORM (Write Once Read Many)
 Compact Disc Recordable (CD-R)
 Compact Disc Rewritable (CD-RW)
 Digital Versatile/Video Disc (DVD)
 Flash memory
Floppy disks
This is a removable disk that has a small storage capacity. It is typically used to store documents so they can be used on more than one
computer. Diskettes are normally used to store backup copies of important information (in case original copy becomes damaged or lost)
and to transfer information from one computer to another. Diskettes are available in two sizes:

Hard Disks/hard drive

This is normally permanently installed and fixed into the computer. However, there are external hard drives available. A hard drive can
access data much more quickly than floppy disk drive. Most important, it can store much more data.

Magnetic tape
A magnetic tape is a tape coated with a magnetic material on which data can be stored. This is a sequential access storage device that is
usually used for backup purposes. Types of magnetic tapes are cassettes, cartridge and reel.

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USB flash drive
A USB flash drive is a very small, portable flash memory that plugs into a computer's USB port and functions as a portable hard drive.
USB flash drives are easy to use, as they are small enough to be carried in a pocket and plugged into any computer with a USB drive.

CD-ROM
CD-ROM is an optical disc capable of storing large amounts of data (up to 1 GB). The CD-ROM has replaced the floppy disk as the media
for software distribution, as it has the storage capacity to hold as much data as 700 floppy disks. Data on this medium can be read but,
unlike the magnetic disk and tape, they cannot be changed (read only).

WORM
WORM disks are non-erasable disks that can offer up to 20GB of storage capacity on a single disk. While WORM disks are very portable,
their inability to erase data written to the disk make this removable storage a favourite for archival purposes, that is, for storage of
historical information.
CD-R and CD-RW
Compact Disc Recordable and Compact Disc Rewritable are types of CDs that allow data to be written to (stored on) discs. CD-R drives
allow users to record information to a CD (compact disc), providing an easy way to archive data or share files. CD-RW discs allow you to
write data to the CD multiple times.
DVD
A DVD is a type of optical disc technology similar to the CD-ROM. A DVD holds a minimum of 4.7 GB of data, enough for a full-length
movie. They are commonly used as a medium for digital representation of movies and other multimedia presentations that combine
sound with graphics. They are becoming increasingly popular as they can store much more data than CD-ROMs. They can store up 17 GB
of data.

FLASH MEMORY

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Flash memory is a non-volatile computer memory that can be electrically erased and reprogramed. It is a technology that is primarily
used in memory cards and USB flash drives for general storage and transfer of data.

We have come to the end of our lecture. See you next week. Remember, if you fail to prepare, be prepared to fail.
Storage devices and interface

In today's lesson, we will be looking at terms associated with storage devices and device interfaces.
Before we do that, let us first look at how data is stored on a diskette.
Data is recorded on a thin, circular plastic disk, coated with magnetic material. Like other magnetic disks, the diskette must be formatted
or divided into areas before data can be written on to it or read from it. Without formatting, there would be no way to know what data
went with what. Thus, in formatting your diskette, your files can be placed in an organised fashion.
TERMS
 Track - A track is a concentric circle on the disk where data is stored. On a diskette, there are 80 tracks on each surface top and
bottom.
 Sector - A sector is a pie-shaped part of a track. Data is recorded along a track within a sector. Each track sector is identified by a
unique address so that every recording location can be identified.
 Cluster - A cluster is a set of track sectors ranging from two to 32 or more, depending on the formatting scheme used.
 Cylinder- A cylinder is similar tracks on a platter of disk.
Diagram to illustrate some of the terms defined above.

Read/Write Head
A device that reads data from and writes data on to a storage media. (You were introduced to this term in the previous lesson but it is
now being highlighted as one of the key terms associated with storage devices.
Movable Heads Disk Drive
These are disk drives that have one read/write head for each surface. The access arms move in and out in order to access the desired
track.
Fixed Head Disk Drive

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These are disk drives that have one read/write head per track. Therefore, if a disk pack has 20 tracks, then each surface would have 20
read/write heads. This reduces the time needed to access records in a particular sector on a track. Figure 2

Figure 2 showing the location of the read/write head alongside its corresponding arm(s).
Access time
After formatting the disk, the read/write heads need to access the stored data in as short a time as possible. Heads are mounted on
access arms that are positioned between the platters. The access time of a read/write head depends on the following:
 seek time - the time taken to move the head to the particular track
 rotational delay - the time it takes the disk to rotate to the particular sector
DEVICE INTERFACES
The device interfaces that are commonly associated with storage devices are SCSI, IDE and SATA. Let us examine each of these device
interfaces.
SCSI

Acronym for Small Computer System Interface, SCSI (pronounced scuzzy) is a set of standards for physically connecting and transferring
data between computers and peripheral devices. SCSI is most commonly used for hard disks and tape drives, but it can connect a wide
range of other devices, including scanners and CD drives. See picture below.
IDE

Acronym for Intelligent Drive Electronics or Integrated Drive Electronics, IDE is an interface for mass storage devices in which the
controller is integrated into the disk or CD-ROM drive. See picture below.
SATA

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Acronym for Serial Advanced Technology Attachment, it is a computer bus primarily designed for the transfer of data between a
computer and mass storage devices such as hard disk drives and optical drives.
Binary representation

How are you with figures? This week's lesson and other lessons to come will require yout o do some calculations. Computers store and
manipulate data numerically using the binary system (reffered to as the machine language), which is comprised of '1' or '0' and, of
course, we will be working with base 2 in our calculations.
Converting decimal numbers to their binary equivalent
To convert decimal numbers to binary, you simply have to divide the number by 2 and subsequently make a note of the remainder. You
will stop dividing when youa rrive at zero. The binary answer is written from the bottom up. Let us now look at an example.
Example 1
Convert 11 from base 10 to its binary equivalent
---> The Base you are working with
---> The decimal number in base 10
Therefore 1110 =
2 11 Remainder
2 5 1
2 2 1
2 1 0
2 0 1
Answer = 10112
* Remember you write your answer from the bottom up!
Converting binary numbers to their decimal equivalent
When converting binary numbers to decimal, for each of the binary digits (bits) you are going to have base 2 raised from 0 to the
corresponding number of bits you have. So, if you have four bits then base 2 will be raised from 0 to 3, example 2 0 - 23. Then, the value
you get when two is raised to the corresponding number is multiplied by its corresponding bit starting from right to left. You then add the
corresponding decimal numbers together to get the decimal equivalent of 10011 2. Let us now look at an example
Example 2
I am going to use the answer we obtained from example one.
Convert 10112 to its decimal equivalent 9This way you can tell if the answer we obtained in example one is correct).
* If you are wondering how we got 20 being equal to 1, remember, anything raised to the power 0 is 1.
23 22 21 20
1 0 1 1
(8 x 1) + (4 x 0) + (2 x 1) + (1 x 1) = 11
Therefore, 10112 = 1110
Binary Addition
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When adding numbers in binary, there are five rules you should apply:
0+0=0
0+1=1
1+0=1
1 + 1 = 10 (This is the binary equivalent of 2, which read as 'one zero' and not ten)
1 + 1 + 1 = 11 (This is the binary equivalent of 3, which read as 'one one' and not eleven)
Example 3
Add the binary numbers 11012 and 11112
11
1 1 0 12
+ 1 1 1 12
1 1 1 0 02
* Please note for 1 + 1, the answer is written as '0' carry '1' and for 1 + 1 + 1 the answer is written as '1' carry '1'.
Subtracting in binary
When subtracting numbers in binary, there are four rules you should apply:
1-0=1
1-1=0
0-0=0
0-1=1
* Please note that in order to subtract 0 -1, we had to take away one (borrow). This one we borrow becomes two (2) because we are
working with base 2. hence, the answer would be '1' as indicated in the rules above.
Example 4
02
1 1/ 0 1 12
- 0 1 1 02
1 0 1 0 12
* Please ensure that you include base 2 in your answers as shown above.
Practice Questions
1. For questions (a) and (b), convert the decimal numbers to binary, and for (c) and (d), convert the binary digits to decimal numbers.
(a) 90
(b) 25
(c) 1010002
9d) 110002
2. Add the following numbers:
(a) 01012 and 00112
(b)01112 and 00102
3. Subtract the following numbers:
(a) 111012 - 00112
(b) 011012 - 00102
We have come to the end of our lesson. See you next week when we will continue to look at binary representation and manipulation.
Remember, if you failt o prepare, be prepared to fail.
System and application software

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The term software is used to refer to the computer programs used in a computer system. Software can be divided into two main
categories:
a) Application programs
b) System programs
APPLICATION SOFTWARE
Application programs are written to solve end-user problems. These include:
 payroll programs - used to generate the payroll of many businesses
 stock control programs - used by businesses to help manage their stock efficiency
 accounting programs - used by businesses to help manage their financial affairs
 educational programs - used in schools for teaching various subjects
 administration programs - used by many organisations for maintaining records of employees, customers, clients, students,
creditors, members etc.
 computer-aided design programs - used by engineers, scientists, architects and others to speed up the designs of buildings.
Aero- nautical engineers may use one to determine how a different tail design may affect the performance of an aircraft
 graphics programs - used, for instance, by an advertising agency for creating advertisements for television
 library control programs - used by libraries for maintaining records of books and borrowers in order to provide faster, more
efficient service
 word processing programs - used by all kinds of people for the efficient preparation of letters, documents and reports
Categories:
 General purpose
 Custom written
 Customisation of general purpose
 Specialised software packages
General purpose application software
General purpose application software is used by a large number of people in a variety of jobs and personal situations. The five main
types of general purpose application softwares are:
 Word Processing
 Spreadsheet
 Database Management
 Communication
 Graphics/Presentation

Advantages of using general purpose software

 You can install it yourself by following the easy instructions in the installation manual that comes with the software
 It is cheaper than employing a programer to write the software for
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  Easy updating and revising since each new version can be had at a reduced price, if the owner can show proof of purchase of
a previous version
 Most users may already be familiar with previous versions of the software so no intensive training programme is required
 Several persons use the software, therefore, help is easy to find
Disadvantages of general purpose software
The package may:
 Be poorly documented
 Have hidden problems
 Not fit the user's need exactly
 Not be user-friendly
Custom written software
If you need a new outfit, you can buy the fabric and take it to a tailor, allow the tailor to take your measurements and then make an
outfit that fits you. Custom written software is one that has been designed or created by a programer to meet the unique need of a user
or organisation. For example, you could hire a system analyst to look at the accounting principles employed by your company and then
set a team of programers to write a program to meet the requirements. This program would be custom written software.

Advantages of custom written software

 The software meets the need of the user specifically
 The software can grow with the company
 Business owners can relieve the stress placed on overburdened employees and save money from hiring additional staff
Disadvantages of custom written software
 Expectations can change midstream when developing custom written software, making a realistic budget difficult to project. As a
result, businesses often run out of money before the project is completed.
 An experienced software team is needed and acquiring the right team can be costly.
 If the people who are trained to use the program resign, then it will be some time before new persons are trained, slowing down
the business functions.
Customisation of general purpose software packages
Imagine buying an outfit in a department store that you like, but it's not exactly your fit. What do you do?
Find a tailor or fashion designer who can adjust it to your size! Similarly, if you find general purpose software in a software house that
you like but it needs some adjustments to meet your specific need, you can get a programer to modify the program to meet your specific
need. A customised general purpose software package is a generalised software package that has been tailored to meet a user or firm's
specific need.
 Areas of the software that can be customised include:
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  Screen colour
 Page size and arrangement on the desktop
 Navigation to available menus

Specialised software packages

Specialised software packages are written for a specific discipline. An example of such packages is expert systems. An expert system is a
type of computer application program that makes decisions or solves problems in particular fields, such as banking or architecture, by
using knowledge and analytical rules defined by experts in the field. For example, a doctor could employ an expert system that asks a
patient a series of questions then make a diagnosis. The software falls into two main categories:
 Business application programs, which are programs that perform the information processing tasks of important business functions
or industry requirements.
 Scientific application programs, which are programs that perform information processing tasks for the natural, physical, social and
behavioural sciences.

SYSTEM SOFTWARE
Systems programs do not solve end-user problems. Rather, they enable users to make efficient use of the computing facilities for solving
their problems. These programs manage the resources of a computer system, automate its operations and make easier the writing,
testing and debugging of users' programs.
Many system programs are supplied by the computer manufacturer since to write them a programmer would need in-depth knowledge of
the hardware details of the specific computer. On the other hand, many application programs can be written with very little knowledge of
the hardware details of a specific computer, and can run on several different computers with little or no modifications.
The most important systems program is the operating system. This actually consists of a number of programs designed to ensure the
smooth running of the computer system. Other common system programs (from the user's viewpoint) are:
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The editor
This program enables users to create files for storing their programs and data. It also provides facilities for making changes such as
adding or deleting lines to files.
Language translators
People normally write programs in what are called high level languages (such as Basic, Pascal , Fortran or Cobol). Before the computer
can run these programs, they have to be translated into the binary code known as the machine language. Each language needs its own
translator. Language translators can be divided into three broad classes: compilers, interpreters and assemblers.
Diagnostic programs
These provide facilities which help users to debug (remove errors from) their programs more easily.
Utility programs
On a typical computer system, there are many routine functions and operations which users may wish to perform. Utility programs
perform tasks related to the maintenance of your computer's health, whether hardware or data. Some of these tasks include: file
management, disk management, backup, data recovery, data compression, anti-virus programs and so on.
OPERATING SYSTEM
An operating system, may be seen as a suite of programs that has taken many functions once performed by human operators. The
sophistication and speeds of modern computers is beyond the capability of human operators to control without the aid of an operating
system. The role of the operating system is, therefore, one of resource management. The primary resources it manages are:
 processors
 storage
 I/O devices
 Data
 Programs
It is quite evident that the operating system controls the way software uses hardware. This control ensures that the computer not only
operates in the way it's intended by the user, but does so in a systematic, reliable and efficient manner. This 'view' of the operating
system is shown below:

Part of the operating system remains in main storage permanently during the running of the computer. This part is called the kernel (or
supervisor or executive) and, as the name suggests, it is the controlling part of the operating system. It controls the running of all other
programs. The remainder of the operating system programs is stored on a direct access storage device from which any particular one will
be 'called' into main storage by the kernel when required.
On many very small microcomputers, the kernel is stored permanently in ROM and starts execution the moment the computer is
switched on. A message is usually displayed by the kernel to signify it is ready to accept commands from the user. On most modern
computers the kernel is not in main storage when the machine is switched on. The system must be booted up. This sometimes involves

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pressing special boot buttons, keys or switches which cause the hardware to load the kernel into main storage from a predetermined
position on a disk.
Functions of the operating system
 In multitasking, where multiple programs can be running at the same time, the operating system determines which application
should run, in what order, and how much time should be allocated for each application before giving another application a turn.
 It manages the sharing of internal memory among multiple applications.
 It handles input and output to and from attached hardware devices such as hard disks, printers and dial-up ports.
 It sends messages to the applications or interactive users (or to a system operator) about the status of operations and any errors
that may have occurred.
 It can offload the management of what are called batch jobs (for example, printing) so that the initiating application is freed from
this work.
 On computers that can provide parallel processing, an operating system can decide how to divide a program so that it runs on
more than one processor at a time.
Choice of operating system
The applications for which a computer is needed largely determines the choice of hardware and accompanying software. The operating
system supplier will need to consider these factors:
 The hardware provision and basic design of the computer
 The applications intended for the computer
 The method of communication with the computer, example, many or few peripherals
 The method of operating the computer
Examples of operating systems include: Windows 1.5 to Windows 7, UNIX, LINUX, DOS, MAC OS and so on.
The choice of O/S is also dependent on the processing environment required by the user. This includes:
 Batch processing
 Time sharing multiprocessing
 Single-user processing system
 Real-time online processing
 Single-user multitasking processing
Batch systems
These are systems that provide multi-programming of batch programs but have few facilities for interaction or multi-access. Commands
or jobs are collected in groups and processed in the order in which they are placed; that is, in a first-in-first-out sequence. Each group of
commands or jobs is called a batch. The jobs are entered in a batch queue and then run one or more at a time under the control of the
operating system. A job may wait in a batch queue for minutes or hours depending on the workload. No amendments are possible during
processing.
System and application software

Time-sharing multiprocessing
The processor's time is divided into small units called time slices and shared, in turn, between users to provide multi-access. These
systems allow the CPU to switch between different programs rapidly, so that users are unaware that they were time-sharing the CPU with
others. Several persons can connect to the main computer via dumb terminals and access different application programs.
Single-user processing system
These systems came on the scene with the advent of personal computers. The majority of small microcomputer-based systems have
operating systems which allow a user to operate the machine in an interactive conversational mode (response to the user's message is
immediate), but normally only one user program can be in main storage and processed at a time; there is no multiprogramming of user

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programs. Multiprogramming occurs when more than one program in main storage is being processed apparently at the same time. This
is accomplished by the programs taking turns at short burst of processing time.
Single-user multitasking
This system only allows one person to use the computer at a time to do multiple tasks.
Real-time processing
This is a system that is able to process data so quickly that the results are available to influence activity currently taking place. There is
often a need for multi-processing. Multi-processing is the name for the situation that occurs if two or more processors are present in a
computer system and are sharing some or all of the same memory. In such cases, two programs may be processed at the same instance.
These systems are used mainly in critical systems. Critical systems are systems where delay in the processing of data after its input can
lead to the destruction of life and property. Examples of critical systems are systems that monitor critically ill patients, nuclear plants,
the engine of an aeroplane, etc.
Utility software
(We made reference to this in our previous lesson).
Utility programs perform tasks related to the maintenance of your computer's health, hardware or data. Some are included with the
operating system, others can be bought as a separate package. Utility programs perform tasks such as:
 File management
 Disk management
 Backup
 Data recovery
 Data compression
 Antivirus programs
USER INTERFACES
The interaction between end-users and the computer is said to take place at the human-computer interface (HCI). The term human-
computer interface is meant to cover all aspects of this interaction, not just the hardware. One of the most important features normally
required in an HCI is that it be user-friendly. As the name suggests, a user-friendly interface is one that the end-user finds helpful, easy
to learn about and easy to use. It is easy to recognise unfriendly interfaces but not so easy to design one that is certain to be user-
friendly.
Types of interfaces
There are many different types of user interfaces available. They may be broadly classified as follows:
 Command-driven interfaces
 Menu-driven interfaces
 Direct manipulation interfaces
 User interface management system (UIMS)
 Special purpose interfaces
 Graphical user interfaces
Note: In some situations, two different types of interfaces may be combined, for example, a menu interface with command options.
Command-driven interfaces
One of the long-established methods by which a user can interact with the computer is by the use of commands. Commands enable the
user to quickly and simply instruct the computer on what to do. However, they require the user to already have knowledge of what
commands are available, what they do and the rules governing how they should be typed, so they are more suited to experienced users
than the end-user. A technical person such as a computer operator or programmer would be familiar with the commands, or where the
end-user continually works with the same program and, therefore, can gain mastery of the commands.

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Advantages of command-driven interfaces
 Faster to use once you have learnt the commands
 For a computer programmer, command-driven interfaces are cheaper to implement
Disadvantages of command-driven interfaces
It is sometimes difficult to remember all the commands, therefore, users have to constantly refer to the software user manual
The user is restricted to using only the keyboard as the interfacing device, while, with other interfaces, a wide variety of input devices
can be used
Commands must be entered at a special location on the screen and in a set format
Menu-driven interfaces
Menus provide another popular form of user interface. There are many different alternative forms of menu. The simplest menus provide
the user with a number of options and a simple means of selecting between them. The user is presented with a choice and, therefore,
does not have to remember any commands. The interface is, suitable for beginners and infrequent users. All the user has to do is to
make a choice. A special type of menu called a pop-up menu; an additional sub-menu pops up as a selection is made. You can click
anywhere on a given document using the right-click mouse button to allow a pop-up menu to appear.
Pull-down menus are a special type of menu used in windowing and were briefly introduced. It is a menu displayed as a vertical list
which hangs from a horizontal bar on the screen in order to elicit a choice from the user.

Advantages of menu-driven interfaces

 The user is presented with a list of options to choose from; they do not need to remember the commands
 Free from typing errors because the user does not have to type the commands
 A wide variety of input devices can be used to interface with a menu
Disadvantages of menu-driven interfaces
 Several steps are required to issue a command
 Once the user has learnt the menu system, it is bothersome to have to wait on the package to present the questions before the
commands can be entered

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Types of wireless media

A wireless network refers to any type of computer network that is wireless and is commonly associated with a telecommunication
network whose interconnections between nodes is implemented without the use of wires. Wireless telecommunications networks are
generally implemented with some type of remote information-transmission system that uses electromagnetic waves such as radio
waves. Examples include:
Satellite
This is man-made equipment that orbits around the Earth or the moon. It acts as a relay station in outer space. It accepts signals beamed
to it from a point on Earth and then reflects the signal to another point. It can transmit data that includes text, voice, pictures and video.

Advantage
 No distance limitation
Disadvantages
 Very expensive to set up
 Not suitable for rapid exchange of data because delays occur when data are sent thousands of miles up into space
Microwave

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These are very high-frequency signals that can be transmitted through space. In this communication channel the medium is not a solid
substance but air itself.

Advantages
 Travels at the speed of light
 Transmits both analog and digital signals
Disadvantage
 Cannot travel around bend
Infra-red
This is a wave of light that is in the area beyond the visible part of the colour spectrum. While it is invisible to the human eye, infrared is
often used to enhance visibility when using night-vision devices.
TYPES OF WIRELESS-NETWORK TECHNOLOGY
Bluetooth
Bluetooth is an open wireless protocol for exchanging data over short distances from fixed and mobile devices, creating personal- area
networks. It can connect several devices, overcoming problems of synchronisation.

Wireless Fidelity (Wi-Fi)

This is a trademark of the Wi-Fi group for certified products based on the IEEE 802.11 standards (which is an organisation dealing with
local-area networks and metropolitan-area networks). This certification warrants interoperability between different wireless devices. Wi-Fi
is used by most personal computer operating systems, many video game consoles, laptops, smart phones, printers and other
peripherals.

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Hotspot
A hotspot is a physical location that offers Internet access over a wireless LAN through the use of a shared Internet connection and a
single router.

Router
A router is a device in computer networking that forwards data packets to their destinations, based on their addresses.

Modem
The term modem is short for modulator - demodulator and is an electronic device that can convert digital signals into analog signals and
vice versa. For example, a modem at one computer converts the digital signals produced by the computer to analog signal for
transmission along a telephone line. The speed of a modem is measured in bits per second (bps). The process of converting digital signal
to analog is called modulation, whereas the process of converting analog signal to digital signal is called demodulation.
Different types of modem

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There are some other terms associated with communication of which you may have heard before such as bandwidth. This term you
might have heard as it relates to communicating via a cellphone. Let us now examine such terms.
Bandwidth
This is a data transmission rate, that is, the maximum amount of information (bits/second) that can be transmitted along a channel.
Types of bandwidth
 Broadband - This is the bandwidth that includes microwave, satellites, coaxial cable and fibre-optic channels. It describes a
technology that provides bandwidth that is greater than that provided by ordinary telephone lines, that is, greater than 64 kilobits
per second. It is used for very high-speed computers whose processors communicate directly with each other. The greater the
bandwidth the greater the data carrying capacity.
 Narrowband - this is a term used to describe data that is transmitted at a slow speed (just over 10 characters per second) for
example, telegraphed transmission.
 Voiceband - This is the bandwidth of a standard telephone line and is used often for microcomputer transmission; the bps is
between 110 and 9600.
Communication modes
The three basic transmission modes or directions are:
 Simplex - This is where data is transmitted in one direction. An example in computing is the interface between the keyboard and
the computer, in that key codes need only be sent from the keyboard to the computer system.
 Half - Duplex - This channel can send and receive data but not at the same time. An example of this would be the use of a
walkie-talkie. Only one end transmits at a time; the other receives.
 Duplex - This is where data can travel in both directions simultaneously. There is no need to switch from transmit to receive
mode as in half duplex. It is like a two-way bridge on a two-lane highway.
Other means of transmission
 Point-to-point transmission - This is a direct link between two objects (such as computers) in a network.
 Broadcast - This is the transmission of data to all connected stations simultaneously.
The Internet
We use the Internet for a number of reasons. Some of these include research, enter-tainment activities (watching movies, music videos,
playing games, etc,) and certainly to visit YouTube or Facebook. Let us now look at the definition of the term and key terms associated
with the Internet.
What is the Internet?
This is the largest computer network system in the world. It consists of many smaller networks connected together by a global public
network. You are familiar with the term Internet, but did you know we also have what is called an intranet and an extranet?
Intranet
This is a private network that belongs to an organisation, and is designed to be accessible by the organisation's members, employees or
others with authorisation.
Extranet
This is when part of an intranet is made accessible to customers, partners, suppliers or others outside a respective company.
Key terms associated with the Internet
Electronic mail (email) - these are mails or messages transmitted electronically by computers over communication channels.
Messages are usually held in a central store for retrieval at the user's convenience.
Advantages:
 Messages are sent instantly, faster and more convenient
 Recipients can store, print, erase, edit or forward messages
Disadvantages
 Email makes it very easy for computer viruses to spread
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  You cannot send email to people who do not have an email account
 You cannot send parcels via an email
Newsgroup
This is an online discussion group. There are over 6,000 discussion groups on the Internet, each group covering a particular
subject or interest. You can read messages from a newsgroup by using a program called a newsgroup reader. Messages are on
several news servers. Newsgroups are periodically synchronised so that a message that is sent to one server can be found on
another.
Internet Relay Chat (IRC)
This allows two or more people from all over the world to participate in live discussions. To participate in a discussion, the user
must have on his/her computer special software (IRC client) and Internet connection. When you type a message, it is sent to the
server and then relayed to the IRC clients of the other people in the discussion. The IRC is a large part of the Internet culture.
Instant messaging programs such as MSN, Yahoo, AOL and ICQ messenger allow people to send and receive messages.
Telnet
This allows you to connect to remote computers over a network called the Internet. Telnet programs activate if your computer is a
terminal that is connected to the remote computer. People or companies can limit the privileges of persons who are logging on to their
computers via telnet.
File Transfer Protocol (FTP)
This is a set of rules used to govern the sending and receiving of files on the Internet. It facilitates the transfer of larger files between
your hard drive and servers connected to the Internet. One of the special features of FTP is that you can continue to download and
upload file interruption, beginning where you left off.
Upload
This is the process of reading data from a user's computer storage and sending it to another computer over communication channels.
Download
This is the process whereby programs or data are transferred over communications channels, from a computer and stored on media
located on the user's computer.
World Wide Web (WWW)

This is just one component of the internet. It is basically a collection of text and media documents called web pages, some of which are
linked.
Web Page
This is a document on the World Wide Web consisting of an HTML file and any related files for scripts and graphics and often hyperlinked
to other Web pages.
Hypertext Markup Language (HTML)
This is a markup language used to structure text and multimedia documents used extensively on the World Wide Web. Hypertexts are
electronic documents that can contain text, tables, graphics, sounds and links to other documents. The links are called hyperlinks.

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Clicking on a hypertext link transports the user to another location on the web. This location can be on the same web page or website or
a totally different website.
Website
This is a set of interconnected web pages, usually including a home page, generally located on the same server, and prepared and
maintained as a collection of information by a person, group or organisation.
Web server
This is a computer that delivers web pages. When a request is made to access a website, the request is sent to the web server. The
server then fetches the page and sends it to your browser.
Web browser

This is a program that allows users to view and explore information on the World Wide Web. Examples of popular browsers are Microsoft
Internet Explorer and Mozilla Firefox. These browsers allow users to view graphics, video, text and animation.
Uniform Resource Locator (URL)
This is a unique address obtained by each page on the World Wide Web. It is basically the address of an Internet file. For example:
www.google.com
Blogging
This is short for Web log. A blog is an online journal or diary of an individual's opinions and latest news. It is updated regularly, in
chronological order.
Hypertext Transfer Protocol (HTTP) - this is a protocol used to request and transmit files, especially web pages and web page
components, over the Internet or other computer network.
Electronic Commerce (E-commerce) - this is commonly known as (electronic marketing) or e-commerce. It consists of the buying and
selling of products or services over electronic systems such as the Internet and other computer networks.
Podcasting - this is a form of audio broadcasting using the Internet; podcasting takes its name from a combination of iPod and
broadcasting. It is a method of releasing files to the Internet, allowing users to subscribe and receive new files automatically.
Bulletin board - this is used as a part of a communication network where users can post messages, read messages posted by other
users, communicate with the system operator and upload or download programs.
Voice over Internet Protocol (VolP) - this is a protocol which governs the transmission of voice over the Internet.
Information misuse

Computers make it so easy for you to collect, store and share information. Likewise, they also make it easy for you to misuse information
or commit computer crimes. For example, information is collected on people who use the Internet, whether they know it or not.
Information may be misused in the following ways:
 By collecting information about people without their permission.
 By vengeful employees or employers who want to spread propaganda on suspecting persons.
 By (willfully or unwittingly) storing incorrect information on an innocent person that may be made available to the public.
 When unauthorised persons are able to view and/or change information.
 By using information for purposes other than those for which it was intended.
Storage of incorrect information
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Whenever data is kept, the owner should ensure that it is accurate and correct. Storage of inaccurate data could result in negative
effects on the individuals and the organisations on which the data is stored. For example, in a credit rating system, if incorrect data
on a consumer is stored, it could be damaging to the consumer, since it might prevent him/her from obtaining credit.
Unauthorised collection of information
A lot of information that is collected is done without the permission of the people involved. Some examples of unauthorised
collection of information are electronic eavesdropping, industrial espionage and surveillance.
Industrial Espionage
Some organisations take on this practice to ascertain pertinent information about their competitors such as their marketing
strategies, research, and future plans to gain a profit or marketing edge. Industrial espionage is when secret information is obtained
by spying on competitors or opponents.
Electronic Eavesdropping
Electronic eavesdropping is the tapping into a communication channel to retrieve information. Data may be encrypted before it is
transmitted to prevent eavesdropping on that data. Hackers commonly use electronic eavesdropping. For example, good hackers
can collect information that you type at websites, such as your credit card number, password or personal data.
Surveillance

The computer-related activities of many people are often kept under surveillance. The information gathered through this surveillance
may be used to develop profiles of several people. Surveillance is not only done by law-enforcement personnel, but many websites keep
you under surveillance as well. Computer surveillance thus involves the use of technology to ascertain information from the user and
from the computer, often without the user's knowledge.
Piracy

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Software piracy is the copying of programs without the consent of the owner. It has become a huge problem for software
manufacturers because it causes loss of revenue and jobs.
Some measures have been put in place to reduce software piracy, including:
 Use of registration keys that are only available with purchase of the software.
 Severe penalties such as heavy fines and/or imprisonment for anyone found selling or knowingly using pirated software.
Measures to reduce misuse of information
There are several ways to reduce the misuse of information. Some of these are:
 Enforcing data protection laws
 Utilising security system
 Keeping information accurate and up-to-date
 Having severe penalties for employees and employers who divulge private information
Data Protection Laws
Every person has fundamental rights when it comes to his/her personal information. Data protection laws generally state that personal
data must:
 Be obtained and processed fairly and lawfully
 Be held for specific purposes
 Be relevant and adequate
 Be accurate and up-to-date
 Not be kept longer than necessary
 Be made available to the individual concerned and provision made for corrections.
DATA SECURITY
Hardware and Data Security
Information is so valuable and important that considerable effort is spent protecting it from theft, fire, viruses, hackers, data loss and
data corruption. Numerous methods are used to protect and secure information. The most widely used of these methods are:
 Using password
 File encryption
 Physical access restriction
 Software access restriction
 Using firewalls
 Back-up and recovery
 Using fireproof cabinets
 Archiving
 Virus protection
Password

A password is a combination of characters used to prevent unauthorised computer access. A person wishing to secure a computer or
individual files on the computer can set a password. In order for access to be granted, the correct password must be entered.
Encryption
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Encryption is the process of encoding information so that it bears no similarity to the original in order to secure it. Files are encrypted
using a key provided by the person who wants to encrypt the information. This key is a combination of characters that are used to tell an
encoding algorithm how to encrypt the information. The encoding algorithm uses a kind of mathematical formula in the conversion
process. In order to read encrypted information, it must first be decrypted. This is the process of decoding encrypted information in order
to obtain the original information.
Physical Access Restriction

Physical access restrictions are used to prevent unauthorised persons from gaining physical access to stored information. The
information may be found on a computer, on a removable storage device or in manual files. Two methods of physical access restriction
are:
 Housing the computer or the removable storage device in a room or building. This area would be secured using locks and a
combination of surveillance cameras, alarms, biometric systems, swipe cards and security guards.
 Locking manual files or removable storage device in a cabinet.
Software Access Restriction
This is quite simply the process of restricting access to software. This may be done using passwords or encryption. However, there is
another method that is fairly popular. Chances are that you have installed recent commercial software and you have been prompted
to enter a serial number (installation key) before the actual installation starts. This is done in an attempt to reduce software piracy
(which you learnt about in the previous lesson).
Virus and Virus Protection
A virus is a malicious program that is designed to corrupt the files on a person's computer and/or prevent the computer from working
properly. Viruses may cause damage to programs and data. People create viruses for vandalism, revenge or mischief. Computers
may be protected from viruses by:
 Avoiding using computers, hard disks, flash drives and so on that are suspected of having a virus.
 Using up-to-date anti-virus software
Email viruses

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An increasing number of viruses are being spread by attachments to email messages. When you open the attachment, your computer
becomes infected. Some of these viruses can even take advantage of the capabilities of email and send themselves to everyone in an
email address book.
Anti-virus software
An anti-virus program (or virus guard) is a special type of software that tries to detect and remove viruses that are on a
computer or removable storage media. Many anti-virus programs allow you to download new virus definitions (information
about how to recognise particular viruses). Advance anti-virus programs, such as Norton Anti-virus, also try to detect viruses
for which there are not yet any virus definitions, by observing programs for suspicious virus-like activity.
Fireproof Cabinets
Despite the fact that we have several security methods to secure data, there is none that can truly protect your data from
natural disasters or fire. Nonetheless, there is a very simple (although low-tech) way to protect manual files and
those on removable storage media from fire. A fireproof cabinet is one such mechanism. A fireproof cabinet is
one that is designed to withstand the high temperatures of fire.
Firewalls
Any file on a network is vulnerable to hackers. However, there are ways to protect computers that are on a
network from hackers. A firewall (in computer terms) is a program that identifies certain weaknesses in networked
computers and tries to prevent them from being exploited. This makes it much more difficult (but not impossible)
for hackers to gain unauthorised access to the computer. Therefore, firewalls help to keep the data on these
computers secure. They are usually installed on computers that access the Internet.
Computer Hackers
A hacker is a person who tries to gain access to areas on networks that he/she is not supposed to have access to.
Hackers may try to:
 Pretend to be someone who has legitimate access to certain areas or files.
 Use extreme attacks (trying thousands of passwords until the right one is found).
 Find weaknesses in the network (known as backdoors) and try to exploit them.
 Corrupt or delete the files being shared.

Backup and recovery

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Sometimes instead of securing data from people who have malicious intent, you have to protect it from your negligence or the fact that
we take for granted that once we save something on a storage medium, we do not need to save it else where. This is what backup and
recovery is for. Backing up data is the process of making a copy of the data and storing it on another storage medium. The storage
media most commonly used for this process are: CD -RW, magnetic tape and external hard drives. If the original data is lost, misplaced
or destroyed, it can be recovered by copying the back-up onto the computer.
Archiving
When data has remained unchanged for a long time and is not accessed on a regular basis, it is said to be inactive. If the data is
occupying valuable space (which is very likely), you might want to store it in a separate location instead. This is what is known as
archiving the data.
Data Corruption
When something causes data to become lost or damaged, this data is said to be corrupted. Data may be corrupted by:
 A computer virus
 Willful acts of employees
 Computer malfunctions
 Poor method of updating data reducing the risk of data corruption:
Reducing the risk of data corruption:
 Minimising the risk of computer malfunction by performing periodic computer maintenance and keeping the computer in a cool
room away from smoke and dust.
 Installing up to date antivirus software
 Using surge protectors and uninterrupted power supply units
Before we begin to look at current trends in technology, try the following past-paper questions shown below.
Question 1
(a) What do the following terms represent?
(i) FTP
(ii) IRC
(iii) E-commerce
(3 marks)
(b) State one advantage and one disadvantage of normal mail over electronic mail.
(2 marks)
(c) Explain the difference between a webpage and a website.
(1 mark)
Question 2
An insurance company gathers medical reports on its clients from the computer system of a certain outpatient clinic. The insurance
company increases its insurance payments according to the number of visits to the clinic. State, with reasons, whether this involves
(a) Electronic eavesdropping (2 marks)
(b) Electronic surveillance (2 marks)
(c) Computer fraud (2 marks)
Question 3
Name one security measure that is appropriate for each of the following situations:
(a) Some papers and books were found in good condition after a fire destroyed the office in which they were stored. (1 mark)
(b) A client was able to obtain a document which was prepared over two years ago. (1 mark)
(c) Only employees in the accounts department are allowed access to salaries and other finances. (1 mark)
(d) After a power failure, the staff was able to use data from the previous day to continue their data entry. (1 mark)
(e) All visitors must sign at the front desk and wear visitor tags. (1 mark)
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CURRENT TRENDS IN TECHNOLOGY

There are many jobs that are done exclusively on the computer. The only thing that forces the employee to travel to the workplace is the
fact that the job entails working with files on the office network. However, with today's technology a person can work files on a remote
network. Telecommuting takes advantage of this technology to reduce unnecessary commuting to and from the office.
Telecommuting
It is the term used to refer to when an employee works off-site (usually at home) using a computer and a communication channel to
communicate with the office network/computer. All that is required is a connection to the office network via a communications channel.
The most common method of doing this is with a modem, telephone line and remote networking software.
Advantages
 Reduced costs from commuting to and from work
 Less stress (from not having to put up with rush-hour traffic) and is more convenient for the employee.
 The employee can work in the comfort of his/her home at his/her own pace
Disadvantages
 The employee may have to absorb resulting additional telephone and electricity costs.
 The initial cost of setting up the computer systems, both at home and at the office, to support telecommuting will be expensive.
 Lack of supervision since the employee can work when he/she wishes, and may be distracted by things such a telephone calls, the
Internet and television.
 There may be a loss of productivity.
 Reduced social interaction between employees.
 Employees will lose out on the possibilityof obtaining a promotion.
Trends in technology

Question 1
(a)(i) FTP - File Transfer Protocol
(ii) IRC - Internet Relay Chat
(iii) E-commerce - Electronic Commerce
(b) Advantage of normal mail over electronic mail (any one of the following):
(i) You can send parcels by regular mail.
(ii) You do not need to have an email address or connection to the Internet.
Disadvantage of normal mail over electronic mail (any one of the following):
(i) Electronic mail is faster.
(ii) Normal mail can get stolen or lost.
(c) A web page is a document on the World Wide Web consisting of an HTML file and any related files for scripts and graphics and often
hyperlinked to other web pages, whereas a website is a set of interconnected Web pages, usually including a home page, generally
located on the same server, and prepared and maintained as a collection of information by a person, group or organisation.
Question 2

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(a) No, this does not include electronic eavesdropping because the insurance company did not tap into any communication channel to
retrieve information.
(b) Yes, this involves electronic surveillance because a computer system was used in order for the insurance company to monitor and
ascertain medical reports of the number of visits made by the clients to the clinic.
(c) Yes, this is computer fraud (any illegal activity done with the use of the computer) because they monitored the clients' visit to the
clinic without their authorised permission.
Question 3
(a) A fireproof cabinet was used
(b) Archiving
(c) Software access restrictions were implemented (password, encryption, etc.)
(d) Back-up and data recovery
(e) Physical access restrictions
CURRENT TRENDS IN TECHNOLOGY
Videoconferencing and Teleconferencing

Both videoconferencing and teleconferencing use the same principle as telecommuting - they use computer technology and
telecommunications channels so that businessmen and women can reduce the need to travel.
Video conferencing is the use of computer, video, audio and communications technology to enable people in different locations to see
and talk to one another.
It is used by organisations to conduct meetings involving individuals who are located at various locations in the world. All that is needed
are computers with microphones and digital video cameras (or webcams) and a communications channel from each location to the next.
The communications channel is usually established using a modem and telephone line.
Advantages of video conferencing
 Videoconferencing offers people the advantage of convenience
 Productivity gains
 Reduced travel time and reduced costs
Disadvantages of video conferencing
 It leads to increased telecommunications costs and a loss of personal contact.
 If the connections are slow, the video and audio may not be of a very high quality.
Teleconferencing is similar to videoconferencing except that there is no video.
Electronic Commerce (E-Commerce)
You were introduced to this term when we looked at the Internet, but we are going to look at it in more details.
Electronic commerce is the buying and selling of goods and services using electronic means to conduct the transactions. However, the
term is commonly used to refer to the process by which commerce is done over the Internet. An example of e-commerce is Amazon.com.
E-commerce generally takes place as follows:

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" A person goes to the website belonging to the person/company offering the desired goods are services.
" On that site he/she would be able to browse through the various products and see descriptions of them. There may also be additional
features, such as links to similar products to the one in which you are interested.
" Once the product(s) are selected, the customer chooses from among two main purchasing options:
1. Paying via traditional methods such as cheque or money order.
2. Paying with a credit card, which is done by entering your credit card number when you are prompted to.
Advantages:
" Customers enjoy increased convenience since they can complete transactions from the comfort of their homes.
" It is also very easy to compare prices from various companies' websites.
" E-commerce also offers features that aren't offered in most stores. At some sites, potential customers can read reviews of products
from people who purchased them. Other sites allow you to download clips from songs on music CDs so you can decide if you like the CD.
" There are many cases where e-commerce can lower production costs, for example in the case of software manufacturers.
Disadvantages:
" The first thing a consumer should worry about is fraud. It is fairly easy for a person to create a website and pretend to be a legitimate
company.
" Internet companies have a tendency to shut down without warning so you may pay money but still not get your product.
" A skilled hacker may steal your credit card number when you type it in at a website. The hacker can then use your credit card number
to make several purchases before you discover that something is wrong. Fortunately, most large companies have measures to address
these issues.
" When making purchases at home, it is difficult to judge the quality of many products without going to the store and holding or touching
the item.
" There is also a reduction in social interaction (even though some people would not see this as a disadvantage). You also do not get
immediate customer service.
Telemarketing
Telemarketing is the use of the telephone as an interactive medium for promotion and sales.
Advantages:
 Increases sales territory (customers can be won nationwide or globally without leaving the home or office) while reducing the cost
of sales visits.

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  Increases efficiency because one can reach more prospects per hour, day and week by phone than can be won with in-person
sales calls.
 Provides an effective way to perform relationship marketing. One can use the phone to stay in touch with existing customers,
introduce new products and make additional sales.
 Allows for interaction and personal selling.
Immediate response to feedback from prospects can be received while still engaged in the sales process. This differs from less
interactive sales methods such as direct mail.
Disadvantages:
 There is a high acquisition cost per sale for purchased prospect lists that typically contain many unqualified prospects. For
example, if one purchases a list of home owners in a particular area, one will most likely have a low number of interested and
qualified prospects. So, making lots of calls will have no yield.
 Telemarketing has become a nuisance to many consumers and has legal ramifications that must be strictly followed.
Computer-Aided Design (CAD)
A computer-aided design (CAD) system uses computer hardware and software in the drawing of engineering or architectural designs. A
CAD package is designed to make it easier to produce detailed plans and accurate technical drawings. It contains software that provides
a set of basic elements such as points, lines, circles, shapes, solids, etc, from which all CAD drawings are constructed.
This offers a considerable advantage over the pencil and paper equivalent since there would be no erasing or redrawing any lines in
order to accomplish this. Also, it is easy to undo any changes that need to be made by simply clicking the 'Undo' button. CAD programs
can produce three-dimensional drawings that can be rotated and viewed from many different angles with the push of a button. In
addition, the computer keeps track of design angles with the push of a button and it keeps track of design dependencies so that when a
value is changed, all other dependent values are automatically changed.
A CAD package can be run on most PCs, but needs a high-resolution graphics monitor to show detail. The input devices required for a
CAD system include a mouse, light pen or digitising tablet for drawing. A special printer or plotter is required for printing design
specifications.
CAD has considerable advantages:
 Designs can be done faster, hence reducing cost.
 It is easier to make changes to the original design.
 It is easier to make duplicates.
 Documentation is generated with the design.
Disadvantages:
 The software is expensive.
 Persons using this software must be competent or have some knowledge in order to be able to manipulate the software.
AutoCAD, SolidWorks and TurboCAD are examples of the CAD software.
Computer-Aided Design and Drafting (CADD)
This is similar to CAD, except that it can be used to produce detailed two-dimensional pictures of objects in addition to the technical
drawings produced through CAD. Unlike the technical drawings, these 2-D drafts are not used as blueprints for the creation of physical
objects.
Computer-Aided Manufacturing (CAM)
Computer-aided manufacturing refers to the use of a computer to control manufacturing plant and equipment in a production system. It
is used in application where precision and accuracy are important, including processors such as welding, paint spraying, cutting and
polishing.
CAM software generates instructions for the computerised control of machines. These CNC (computerised numerical control) machines
include computerised lathes for turning and drilling and machines for cutting and polishing large stones for building purposes.
The advantages of CAM include:
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  Faster production of parts and products.
 Production of a more consistent product.
 The ability to better control and maintain the quality of a product.
CAM is often used in association with CAD.
Hardware
 Robots
 Process controls, for example, temperature regulator, flow meter and viscometer
 Mainframe, minicomputers and microcomputers
 Graphics plotters
CAD/CAM systems
These systems are used in the design and manufacturing of products. Engineers use the system to create the product designs, and then
to control the manufacturing process. Two CAD/CAM software packages currently available are SolidWorks and MasterCAD. They can
create drawings, model trajectories (develop and work out the movement) of cutting tools and develop numeric-control and processing -
centre programs. They support 3-D modelling, sheet-metal punching and bending, and plasma and laser cutting.
Trends in technology (Part 3)
Natalee A. Johnson, Contributor
Hello, students. In this week's lesson, we will conclude looking at current trends in technology.

Computer-aided engineering (CAE)

CAE systems analyze engineering designs produced by CAD systems by simulating a variety of conditions to see if the design actually
works. CAE features are found in most CAD packages. Two CAD/CAM/CAE packages currently in use are Unigrapics and hyperMill.
Expert Systems
Consider what happens when you go to the doctor. The doctor asks you a few questions and runs a few tests then uses the information
obtained from these to make a diagnosis. Doctors can do this because their minds act as a sort of database that has information about
which symptoms correspond to which illnesses.
Definition:
Expert system is software that imitates experts such as doctors by comparing responses to certain questions to those in a database in
order to make a diagnosis or recommendation. An expert system is useful in providing support for making decisions and can also
'suggest' alternatives or other issues to be considered.
It consists of two parts: the knowledge base and the inference engine. The knowledge base contains a large volume of information in a
particular field - for example, the different types of diseases, symptoms and possible treatments. The inference engine of an expert

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system analyses the input data using 'reasoning' methods and the knowledge base to arrive at a conclusion. It also provides the user
with an explanation of how it arrived at its conclusion by showing the concepts that are used.
Advantage
 Expert systems do not make biased decisions or incorrect decisions based only on the information supplied.
Disadvantages
 An expert system is incapable of making moral judgements.
 They are limited to certain areas of expertise and cannot adapt as a human would in light of new medical developments (without
first being reprogrammed). An expert system is, therefore, no substitute for human intelligence.
Hardware
 Sensors
 Process controls
Software
 Simulation software
 Software for the expert systems
A medical expert system has the following advantages:
 It gives support in making decisions about which a doctor may be doubtful because of a lack of knowledge or lack of experience.
 It can help experts arrive at an accurate solution much faster.
 It can show the concepts it uses to arrive at its conclusions.
It also has the following disadvantages:
 It lacks intuition which is sometimes vital in decision making.
 It cannot learn from mistakes
 It could have disastrous effects if used by unqualified individuals.
Robots
Robots are computer-controlled machines that include functions such as locomotion, mobility, grasping and recognition. A
robot's central processor might be a micro-processor embedded in its shell, or it might be a supervisory computer that controls
the robot from a distance. In any case, the processor is functionally identical to the processor found in a personal computer, a
workstation or a mainframe computer.
The most important hardware differences between robots and other computers are the input and output peripherals. Instead of
sending output to a screen or a printer, a robot sends commands to joints, arms and other moving parts. Most modern robots
include some kind of input sensors. These sensing devices allow robots to correct or modify their actions based on feedback
from the outside world.
At present, robots are mainly used in the following areas:
 Manufacturing industries
 Automotive industries
 Assembly lines for welding, paint spraying, assembling and loading.
 Electrical and electronic industries - they are used for assembling and installing various parts in the manufacturing of video
cameras, personal computers and many other devices.
Advantages
 Robots are excellent at performing repetitive tasks that require high precision and accuracy.
 They can perform more work with fewer errors, and they don't get sick, complain or take strike action.
 Robots are also able to operate in extreme environments where it might be difficult or impossible for human beings to operate.
 Specialised robots have been developed for a number of tasks.
 Remotely operated vehicles (ROVs) are able to perform tasks such as searching for and recovering ship and plane wreckage,
specialist scientific studies and the burial and repair of underground telecommunication cables.
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  Other robots clean up hazardous waste sites and handle wastes that might be too dangerous for humans.
 Robots decontaminate and dismantle radioactive devices and measure levels of radioactivity at waste sites.
 Robots mine for metal and coal.
 Robots deactivate bombs.
Now that we have concluded looking at current trends in technology, try the following revision past-paper questions:
1. The increase in the level of computerisation in offices, together with the decrease in the cost and the availability of data
communication services has created new ways of conducting business. Some employees now have an opportunity to perform their work
from home by a process known as 'telecommuting'.
(i) State two items of hardware that an employee must have if he/she is telecommuting.
(ii) State two advantages of telecommuting to the employee.
(iii) State one disadvantage of telecommuting to the employee.
(b) Explain how telecommuting is different from both teleconferencing and telemarketing.
2. (i) What is an expert system?
(ii) Name one area in which expert systems are used.
(iii) Give one advantage and one disadvantage of using expert systems in the area named at (ii) above.
3. (i) What is meant by the terms 'CAD' and 'CAM'?
(iii) Why are CAD and CAM usually integrated?
4.(a) Describe briefly an application in which a robot (or robotic arm) is used in an industry, stating clearly one function that the robot
performs.
(b) State two advantages of using robot (or robotic arm) over using a manual method in the application described in part (a) above.

Problem solving and program design

Have you ever wondered how problems are solved on the computer, or why we ourselves have problems we cannot seem to solve? Well,
you are going to be requiring your analytical skills with some mathematical knowledge for this unit.
In our everyday life, we actually solve simple problems. For example, you have a problem getting to school early in the morning. How
would you solve this problem?
 Examine the problem
 Determine possible solutions to the problem such as setting an alarm clock; making arrangements with a taxi to pick you up early,
travelling with a friend who is normally early for school or getting ready for school earlier.
 Evaluate to determine the best possible solution to the problem
 Choose the best solution to your problem
Similarly, the computer is designed to solve problems for you, the user. How is this possible? A computer solves end-user problems by
following a set of instructions given to it by the programmer which produces the specified results. The computer programmer creates the
instructions for the computer to follow. These instructions are referred to as computer programs. You were introduced to the term
computer programs when we looked at software.
A computer program is a finite set of clear and specific instructions written in a programming language.
Problem-solving on the computer
The design of any computer program involves two major phases:
 The problem-solving phase
 The implementation phase
The problem-solving phase comprises the following steps:
1) Define the problem

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2) Find a solution to the problem
3) Evaluate alternative solutions
4) Represent the most efficient solution as an algorithm (you will learn about this in up-coming lessons)
5) Test the algorithm for correctness
The implementation phase comprises the following steps:
1) Translate the algorithm into a specific programming language
2) Execute the program on the computer
3) Maintain the program
Defining the problem
Defining the problem is a way to help the programmer understand what he or she is required to do. It involves breaking down the
problem into three key components:
 What is given (that is, the inputs)
 The expected results (that is, the output)
 The tasks that must be performed (that is, processing)
These three components can be illustrated using what is called a defining diagram. Some texts may refer to this as the input processing
and output (IPO) chart. The defining diagram is a formal approach to defining a problem. The defining diagram is a table with three
columns, which represents the three components: input, output and processing.
The Input
The input is the source data provided. You can identify what is the input in a given problem by the following keywords: given, read or
accept.
The Output
The output is the end result required. You can identify what is the output in a given problem by the following keywords: print, display and
output.
The Processing
The processing column is a list of what actions are to be performed to achieve the required output.
Let us now look at an example of a problem that is defined with the construction of a defining diagram.
EXAMPLE 1
A program is required to read three numbers, calculate and print their total.
Defining Diagram:
INPUT PROCESSING OUTPUT
3 num 1. Read/get 3 nums TOTAL
Say num1, 2. Add numbers
num2, together
num3 3. Print total
We will break here to look at the solutions to the revision questions I gave you in the previous lesson.
1. (a)(i) modem, telephone, fax machine
(ii) Reduction in travel expenses/fuel consumption
- Working men and women would be able to spend more time with their families
(iii) The worker might miss out on promotion opportunities at central headquarters
- Increase in expenses such as telephone, electricity, etc.
(b) Telecommuting involves working off-site/home and communicating with the office, while teleconferencing and telemarketing do not.
Telemarketing is the use of the telephone as an interactive medium for promotion and sales to prospective customers, while
teleconferencing is used by organisations to conduct meetings involving individuals who are located at various parts of the world.
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2. (i) An expert system is a program that reproduces the knowledge and thought processes of human experts in certain well-defined
fields.
(ii) Areas of application - any one of the following:
(a) Medicine - diagnosis of infectious blood diseases, prescription of medicine
(b) Geology - search for mineral deposits
(c) Chemistry - identifying molecular structure of compounds
Advantages:
 Does not display biased judgements
 Does not jump to conclusions on the face of contrary evidence
 Systematically considers all possible alternatives
Disadvantages:
 Not good at judgement requiring common sense
 Cannot adapt easily to new rules and concepts
 Cannot reason across disciplines
3. (i) CAD - Computer Aided Drafting/Designing - A system that uses computer hardware and software in the drawing of engineering or
architectural designs.
CAM - the use of a computer to control manufacturing plant and equipment in a production system to produce a product.
(ii) CAD and CAM are integrated so that an object is designed, tested and then passed to a manufacturing process.
4. (a) Robotic arms are used in the manufacturing of motor vehicles. One function that the robotic arm serves is to spray the motor cars
with a uniform coat of paint.
(b)(1) Robots do not miss
(2) It wastes less than half as much paint as a human painter does
(3) They are not affected by the dangerous fumes or heat, therefore, they do not get sick
Problem solving and program design (Part 2)

1. Identify the input (that is, the data that is given). The keyword, read, identifies the input as three numbers, that is, any three numbers.
2. Identify the output. The keyword, print, identifies the output as the total (or sum) of the three numbers.
3. List the processing steps. Here, we list all the actions that must be performed in order to get the desired results. For example: What do
we have to do to the three numbers in order to print their total?
1. We must first get the numbers.
2. We must then calculate their sum.
3. We must then print the total.
Key things to note
1. In the defining diagram, the actions must be in a logical, sequential order.
2. All the necessary actions must be explicitly stated. For example, the read action and the print action must not be assumed.
3. The processing section is not the solution to the problem. It is simply a list of the things that must be done in order to solve the
problem.
EXAMPLE 2
Given three integers representing the age of three boys, respectively, write a program to find their average age and also determine the
age of the oldest boy.
Defining Diagram
INPUT PROCESSING OUTPUT
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3 integers
Average-age
1. Read/accept/get 3 integers Highest-age
2. Find the average of the 3 integers
3. Find the highest age
4. Print average, highest age

Practice Questions
Use a defining diagram to answer the following:
1. A program is required to read two numbers. Calculate and print their difference.
2. A program is required to read the length and width of a rectangle. Calculate and print the area and perimeter of the rectangle.
PROGRAM DESIGN
After defining the problem, based on the steps of the problem-solving phase, you find a solution to the problem. In finding a solution to
the problem, you have to also analyse alternative solutions to the problems. When we are solving problems on the computer, this is done
by representing the most efficient solution as an algorithm. Before we look at the term algorithm, there are some key terms you must
first be familiar with. They are variables, constant and data types.
When you ask the computer to read two numbers, find the sum of the two numbers then output the sum. When the computer reads the
two values, it has to store them somewhere in memory. Similarly, it will have to store the value of the sum somewhere in order to
provide an output to you, the user. These values are normally stored in what we call variables.
 A variable is a named location in memory that stores a particular value. This value may be changed during the execution of a
program. Examples of variable names include 'number', 'age', 'name', 'length' and so on. You can have several different names,
numbers, ages etc.
 A constant provides locations for storing data which do not change value during execution of a program. For example, if you were
calculating the perimeter of a circumference, you will need to include PI which is normally 3.17 in your calculation. In the formula,
PI would remain constant.
 Data types:
Variables typically store values of a given type. There are several data types but we will be focusing primarily on the following data
types: integers, floating point (real), characters and strings.
 Integers
Used to store whole numbers (whether negative or positive) for example, 2,-6, etc.
 Floating point/Real
Used to store real or fractional numbers for example, 2.5, 3.50 etc.
 Characters
Any single character in the ASCII set (a single character such as a letter of the alphabet or punctuation) for example, 'A'.
 String
A collection of characters such as a word, phrase or sentence for example, Mary.
ALGORITHMS
An algorithm is a sequence of precise instructions for solving a problem in a finite amount of time.
Properties of an algorithm:
 It must be precise (exact)
 It must be unambiguous (in other words it must be clear)
 It must give the correct solution in all cases
 An algorithm must terminate or eventually end

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The algorithmic structure
Every algorithm should have the following sections, in the stated order:
Header:
Algorithm's name or title
Declaration:
A brief description of the algorithm and variables used. That is, a statement of the purpose as
well as initialisation of the variables.
Body:
Sequence of steps
Terminator:
An end statement
Algorithms

Students, in this week's lesson, we will continue to look at algorithms. Before we do so though, here are the solutions to the defining
diagram questions I gave you in the previous lesson.
Question 1
INPUT PROCESSING OUTPUT
2 numbers 1. Read/accept/get 2 numbers
2. Subtract the two numbers Difference
3. Print Difference
Question 2
INPUT PROCESSING OUTPUT
Length, Width 1. Read/accept/get length and Area
Say L, W width of rectangle Perimeter
2. Find the Area of the rectangle
3. Find the perimeter of the
rectangle
4. Print Area, Perimeter
The algorithmic language
When writing algorithms, the language gradually progresses from English towards a notation that resembles that of a programming
language. An intermediate notation called pseudo-code is commonly used to express algorithms. A pseudo-code is an imitation computer
program written using mathematical notations and English-like statements to describe the logics to solve a problem or carry out a
procedure. The pseudo-code is used as a guide to code the solution to the problem in a high level language.
Parts of a pseudo-code algorithm
A pseudo-code algorithm contains one or more of the following statements:
 Input Statements
 Assignment Statements
 Output Statements
 Control Statements (Sequence, Selection, Repetition)
Do's AND DON'Ts WHEN WRITING PSEUDO-CODE
You should do the following:

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  Use the assignment symbol (?) in assignment statements instead of the equal sign
 Use the equal sign for conditional statements (if statements)
 Use meaningful variable names
 Use indentation to show the logic and scope of control structures
 Insert comments to clarify meaning of blocks of code
You should not do the following:
 Use language-specific constructs such as case, switch statements or for loops in the pseudo-code.
Constructs such as while, repeat and if-then-else are sufficiently general and can, therefore, be used in the pseudo-code.
Keywords such as readln, writeln, printf, scanf should not be used. These are used for high-level languages.
 Attempt to write Pascal code before writing the algorithm. That is, do not execute the program first and then try to write the
algorithm afterwards, based on the program code. This is a very bad practice and is essentially a waste of time.
Parts of a pseudo-code algorithm
Input Statements
The input statement is used to get data from outside the computer from a particular input device into a variable for manipulation by the
pseudo-code. The key words we will use for input will be "input" or "read".
To read data into a variable, you write the word input or read followed by the variable name.
This is the way in which it will be written: Read variable_name
The variable_name is the name given to the location where the value is to be stored. For example, if I am reading a number into a
variable, my variable name would be "num" and the read statement would, therefore, be:

Output Statements
The output statement is used to get information to the programmer or to the user. The key words we will use for output are: "display",
"print" and "output". To output information to the user you write the word Print, a statement followed by a variable_name or the word
Print followed by a variable_name.
This is the way in which it will be written: Print "statement", variable_name or Print variable_name
For example, if you were required to read two numbers, find the sum of the numbers and output the sum of the numbers. The output
statement would be:

Control statements
Natalee A. Johnson, Contributor
Students, in this week's lesson, we will continue to look at algorithms and flow charts.
Sequencing
Sequencing is a part of any programming structure. This is where the program is viewed in a simple top-to-bottom manner, from the
input statement to the end of the program. Example 1 (product program) given in the previous lesson is an example of a basic program
written in a sequential manner.
Before we look at the selection statement, below are examples of how the various control structures are depicted in a flow chart.
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Selection/Conditional statements
In our everyday lives we make simple and important decisions. These decisions are normally based on a particular condition. For
example, if school is keeping, you will attend; if it is not keeping, you will stay home. The decision will be made based on the condition of
whether or not school is keeping.
The if statement
The if-statement is a conditional statement. It causes execution of some statement to depend on the truth value of a certain condition
given as a Boolean expression. A Boolean expression is an expression that results in a value that is either true or false. For example, the
expression 2 < 5 result would be true because the number 2 is, indeed, less than the number 5.
If the condition is true, then the statements immediately after "then" are executed; if it is false, then the statements after 'else' are
executed, provided that the "else" clause is present.
Example 1
if school is in Example 2
session(condition) then if school is in session then
______ attend school (statement ______ attend school (statement
executed after then) executed if true)
endif else
______ do not go to school (Statement
executed if false)
endif
As observed in the examples above, the 'if statement' structure begins with an "if" and ends with the word "endif".
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Let us look at a pseudocode algorithm that will show sequencing and selection as well as the flow chart version of the program.
Example 3
Write a pseudocode algorithm to read two numbers and to print the value of numb1 if it is greater than numb2 else print numb2.
Psuedocode version
Algorithm Comparison of the bigger value of two variables
Start
read numb1, numb 2
if numb > numb2 then
___ Print numb 1
else
___ Print numb2
end if
Stop
Flowchart version

Loop (Repetition)
Most of the things we do in our everyday life require some form of repetition, like getting ready for school or work. You perform the same
steps over and over five to seven days a week.
When we want the computer to repeat some statements several times, we need a loop structure or a loop in the pseudocode to instruct
the computer on what to repeat and how often these steps are to be repeated.
Every loop has four major elements. These are:
 Initialisation
 Repetitive statement(s)
 Loop statements (block)
 Conclusion
 Control statements (Part 2)

 Hello students. In this week's lesson we will continue to look at control statements and flow charts.

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  Initialisation
 Before a loop is started, we may need some statements to get started. For example, we may need to initialise a variable to a start
value or read an initial value into a variable.
 Repetitive Statements
 These are the statements that the computer will repeat.
 Loop Block
 We must specify what statements are to be repeated by the computer. The repetitive statements are normally placed in the loop
block.
 There are three main types of loop constructs and they are: For Loop, While Loop and Repeat Until. Let us now examine each of
these loop constructs.
 The For Loop
 The For Loop syntax is shown below:
 For Control_Variable <----------- <start value> to <final value> Do
________ Block Statement(s)
Endfor
 The 'for' loop is an example of a definite loop. It facilitates the repetition of a block of instructions a definite number of times. Let
us look at an example of having a bowl of soup with a spoon; you could have at least 20 sips of the soup. The algorithm would
look something like this:

 Please note, you use the 'for loop' when you have a block of statements that will be carried out a set number of times. Otherwise,
you use a different loop construct.
 Example 2
 Write an algorithm to read 10 numbers and output the sum of the numbers.
 Pseudocode version
 Algorithm Sum
 This program will read 10 numbers and find the sum of those numbers.
 Sum <---------- 0
 For counter <-------- 1 to 10 do
______ Read number
 Sum <---------- Sum + number
 Endfor
Print "The sum is", Sum

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  Key things to note when working with loops:
 The use of an accumulator
 In example two shown above, the 'for loop' example, we were required to find the sum of 10 numbers. You
would agree that it would be time consuming to sit and memorise the 10 numbers entered in order to add
them.
 With the use of an accumulator you do not need to write down or try to memorise the numbers. As in the
case of the 'for loop' you can start the sum with the value 0, and each time you are given a new number you
add it to your present sum.
 Hence, the statement: Sum <----- Sum + num, if the first number entered is 40, your sum would be 40.
Therefore, Sum <----- Sum + num, would be Sum <----- 0 + 40 = 40.
 If you then add another number, say 10, to your present sum, your new sum would be 50.
 Sum <---- Sum + new number
 Sum <---- 40 + 10 = 50
 The process will continue until all the numbers have been totaled. The only value you will keep in your
memory is the current sum.
 Counters
 This is the process of counting the number of times a value is entered or a statement is carried out. You can
also allow your counter to begin at 0 and then increment (increase accordingly). Here is an example of an
assignment statement with use of a counter.
 Counter < ----------- 0
 Counter < ------------ Counter + 1
 In the example above, the counter is initially set at 0, which means that every time the assignment
statement is executed, the value of the counter variable is increased by 1. Thus, the assignment statement
will provide a mechanism for counting. Using the same for loop example, a counter would count and keep
track of the 10 numbers which would be entered and then totaled. Such that only 10 numbers will be
entered.
 Control statements (Part 2)

 Students, in this week's lesson, we will continue to look at control statements and flow charts.
 The While Loop
 The While Loop syntax is shown below:
While Variable not equal to Control_Variable Do
 ____ Block Statement(s)
Endwhile
 The While Loop is an example of an indefinite loop. It facilitates the repetition of a block of instructions until a certain condition is
met. No one knows exactly how many times the block statements (instructions) will be carried out. Using the same example of
having a bowl of soup with a spoon, no one can tell how many sips you would have to take to fill your stomach. It depends on the
size of your stomach and the size of the spoon. The algorithm would look something like this:
 Example 1

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  Please note that you use the While Loop when you do not know exactly how many times a block of statements will be carried out.
In this case, there will be some terminating condition.
 Example 2
 Write a pseudocode algorithm to read a set of integer numbers terminated by 999. The pseudocode should find the sum and
average of the numbers. The algorithm should also output the sum and average of the numbers.
 Pseudocode version
 Algorithm Sum and Average
 This program will read a set of integer numbers and calculate the sum and average of the numbers.
 Sum <-------- 0
 Counter <---- 0
Read number
While number <> 999 do
____ Sum <-- Sum + Number
 ____ Counter <--- Counter + 1
 Read number
 * This is the block of instructions that will execute. Sum will continue to increase, counter will increment and the program will
continue to read a number until the condition is met, which is when the user enters 999 and the program will end or terminate.
 The symbol <> is a logical operator which means 'not equal to'
 Flowchart version

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  The Repeat - Until Loop

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  The Repeat - Until Loop syntax is shown below:
 REPEAT
 Block Statement(s)
 UNTIL (condition)
 or REPEAT
 Block Statement(s)
 UNTIL <condition is true>
 The Repeat-Until Loop is similar to the While Loop except that the condition is tested at the end of the loop. Thus, the block of
statement(s) will continue to execute as long as the specified condition in the UNTIL statement is false. Using the same example
of having a bowl of soup with a spoon, you would continue to sip your soup as long as you have soup in your bowl.
Control statements (Part 3)
Students, in this week's lesson, we will conclude looking at control statements and also look at trace tables.
The Repeat - Until Loop
Here is an example to illustrate the explanation I provided in the previous lesson on the repeat loop.

When constructing a solution to a programming question that contains a loop, ask yourself the following questions:
 What type of loop do I need, is it a Definite or Indefinite?
 Does the question require any input? Yes or no? If the answer is yes, then for a 'For Loop', your first input statement must take
place somewhere immediately following the beginning of the loop. If your loop is a 'While Loop', then you will have to use an input
statement:

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 - before the beginning of the loop (pretest)
- towards the end of the loop (post test)
 Do I need to count anything? If yes, how many? For each item to be counted you need to initialise each counter variable before
the start of the loop and you need to put each counter construct inside the loop.
 Do I need to sum or accumulate any value? Do I need a product, average, etc. If yes, how many? For each value to be
accumulated you need to initialize and accumulator to 0 outside the loop and you need to place an accumulator construct inside
the loop.
 Is there any condition or conditions specified by the questions? If yes, for each counter, accumulator or print statement within the
loop block, ask yourself under what condition does it do this?
 Do I need to print anything? If yes, where do I put my print statement? Inside the loop or outside the loop? A print statement
placed inside a loop will be executed (carried out) each time the loop block is repeated.
 What action must I perform when the loop terminates? You may need to calculate an average, a difference or print a value.
PRACTICE QUESTIONS
1. Write a pseudocode algorithm to read a set of grades (terminated by -1) and print their average as well as the highest grade received.
2. Write a pseudocode algorithm to read a positive integer N followed by N integers. For these N integers, the algorithm must count and
print the number of zero and non-zero values.
3. Write an algorithm to read the names and ages of 10 people and print the name of the oldest person.
Assume that there are no persons of the same age.
TRACE TABLE
A trace table is an important tool for testing the logics of a pseudocode for correctness. A trace table is a rectangle array of rows and
columns. The column headings are the variables in the pseudocode. As instructions in the pseudocode are carried out and the variables
are modified, the changes are recorded in the appropriate column in the table. When the pseudocode terminates, the final values in the
trace tables should reflect the correct result.
Let us look at an example of how a trace table is executed using example 1 shown below.
Example 1
Write a pseudocode algorithm to read a set of positive integers (terminated by 0) and print their average as well as the largest of the set.
Numcount <---- 0
Sum <----- 0
Largest <---- 0
Read Number
While Number ntot equal to 0 do
___ Sum <---- Sum + Number
___ Numcount <---- Numcount + 1
If Number > Largest
__ Largest <---- Number
Endif
Read Number
Endwhile
Average <--- Sum/Numcount
Print Average, Largest
The Trace Table for example one
Example 1
We will use the following numbers as input for the trace table: 2, 5, 6, 1, 10 and 0.

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  For the example above, you will first initialise your variables as shown in the algorithm.
 Then you would repeat step 2 to step 5 until the user enters '0'. The program will then stop.
 The average will be calculated (24/5), average is 4.8
 Both the average and the largest value will be printed which is 4.8 and 10, respectively.
 Relational operators and truth tables

 The relational operators are used for comparison of the value of one element with another. There are six types of relational
operations: equal, greater than, less than, greater than or equal to, less than or equal to, and not equal to. Each of these
operations can be used to compare the values of the variables. The result of each of these operators is either true or false. When
using these operators, make sure all the arguments are the same data type. Integers should be compared with integers, strings
with strings, and so on. Table 1 reviews each of these operators.
Table 1 Relational Operators
Operator Name Symbol Descrption
Equal = Returns true if both sides are equal.
Returns true if the variable on the left
Greater than >
isgreater than the variable on the right.
Returns true if the variable on the left
Less than <
isless that the variable on the right.
Returns true if the variable on the left
Greater than or equal to >= isgreater than or equal to the value of
the variable on the right.
Returns true if the variable on the left
Less than or equal to <= isless than or equal to the value of the
variable on the right.
Not equal to <> Returns true if both sides are not equal
 TRUTH TABLES
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  A truth table is a good way to show the function of a logic gate. Logic gates process signals which represent true or false. A truth
table shows the output states for every possible combination of input states. The symbols 0 (false) and 1 (true) are usually used in
truth tables. There are three main logic gates we will concentrate on for the CSEC level and they are: AND gate, OR gate and the
NOT gate. For every Logic gate, we are going to be examining its corresponding truth table.
 AND GATE
 For the AND gate, the output Q is true if input A AND input B are both true: Q = A AND B
An AND gate can have two or more inputs, its output is true if all inputs are true.

 OR gate
 For the 'OR gate', the output Q is true if input A or input B is true (or both of them are true): Q = A or B
An OR gate can have two or more inputs. Its output is true if at least one input is true.

 NOT gate (inverter)

 The output Q is true when the input A is not true, the output is the inverse of the input: Q = not A
A NOT gate can only have one input. A NOT gate is also called an inverter.

 Here is the solution to the practice questions you were given in the previous lesson.
 1. gradecount <--- 0
highest <--- 0
read grade
zerocount <--- 0
 while grade <> -1 do
sum <--- sum + grade
gradecount <---- gradecount + 1
if grade > highest

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 highest <---- grade
endif
 read grade
endwhile
 Average <---- Sum/gradecount
Print Average, highest
 2. Sum <---- 0
count <----- 0
noncount < --- 0
Input N
 repeat
input number
if number = 0 then
zerocount < --- zerocount + 1
endif
if number <> 0 then
 noncount < ---- noncount + 1
endif
 count <---- count + 1
until count < ---- n
print zerocount, noncount
 3. Oldage < ---- 0
Oldperson <---- " "
For j <---- 1 to 10 do
Read Name, Age
 If Age > Oldage then
 Oldage < ---- Age
Oldperson < --- Name
 Endif
 Endfor
 print "The oldest person is", Oldperson
Top-down design approach

Use of the top-down design approach to Problem Solving

You have learnt in previous lessons the way in which you solve a problem on the computer and you have been learning thus far how to
write your pseudocodes and how to construct your flow charts. Now you are going to learn about a technique that can be employed when
you have a big program to code or problem to solve. This method is called the Top-down Design Approach to programming.
What is Top-Down Design?
The Top-Down Design Approach or Modular Programming, as it is sometimes called, involves breaking a problem into a set of smaller
problems, called sub-problems or modules, followed by breaking each sub-problem into a set of tasks, then breaking each task into a set
of actions. This is called a 'divide and conquer' approach.
When faced with a complex problem, it is easier to break the problem down into smaller, more manageable sections and tackle each
section as a separate entity, rather than trying to solve the large problem in one go.

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Below is a diagram depicting a typical Top-down Design or modularity approach to programming.

As you may observe with the diagram above, there is a Major Problem which has been broken down into two sub-problems. The sub-
problems are then broken down into respective tasks of which certain specific action(s) will be carried out.
A sub-problem is a set of related tasks. A task is a set of related actions. An action is a basic instruction that needs no further refinement.
For example, an action might be a simple instruction such as subtract two numbers. The process of dividing the problem into sub-
problems or modules and breaking them down into smaller units is called stepwise refinement.
One advantage of modular programming is that when a problem has been decomposed into smaller sub-problems, each sub-problem can
be solved as a single entity. However, the solution of each individual sub-problem does not necessarily solve the larger problem. There
must be cohesion between the modules. That is, there must be a mechanism for communicating between the different sub-problems.
Let us now look at an example that will explain the concept of Top-down Design with stepwise refinement and you will see how we
represent the sub-problems in a hierarchy chart and then how we establish communication between the various modules.
A hierarchy chart is a tree-like structure that shows visually the relationships between the modules of a program. The root of the tree
(the top box) represents the controlling or main module. The next level shows the modules that are called directly by the main module,
while the next level shows those modules which are called by the ones above them, and so on and so forth.
Example 1
You are required to write a program that will read two numbers find the sum, product and difference of the two numbers then output the
respective results.
Six sub-problems can be identified here:
1. Sub-problem 1: read two numbers
2. Sub-problem 2: find the sum of two numbers
3. Sub-problem 3: find the product of two numbers
4. Sub-problem 4: find the difference of two numbers
5. Sub-problem 5: output the results
The hierarchy chart for the modules above would look something like this:

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The main module will read the input data and then pass it to each of the sub-programs. The subprograms will, in turn, perform their tasks
and return the results to the main module where they will be printed.
PROGRAMMING LANGUAGES
Programming languages fall into the following categories:
 Machine Language/1st Generation
 Assembly Language/2nd Generation
 High-level Language/3rd Generation
 Fourth-Generation Language
These languages can be further categorized as either being low-level or high-level languages.
Low Level High Level
 Machine Language  High-level Language
 Assembly Language  Fourth-generation Language
Let us now examine each of these languages.
Machine Language
This was the first language available for programming. At the machine level, the instructions are written in ones and zero (binary digits).
This is the only language that the computer understands.
Advantages:
 Programs execute fast
 Efficient use of memory
Disadvantages:
 Programming is slow and tedious
 Code difficult to learn, read, understand and correct
 Code is machine specific, that is, it cannot be used in the same form on other computer models
Assembly Language
These were developed to replace the zeros and ones of machine language with symbols that are easier to understand and remember. It
uses special codes called mnemonics (words that suggest meaning) to represent machine language instructions. For example:
 MOV represents Move  HlT represents Stop
An assembly language is translated into a machine language by using a translator program called an assembler. However, both the
machine language and assembly language programs are machine dependent, that is, the way the program is written depends on the
operation of the computer.
Advantages:
 Programming faster and less tedious than for machine language.
 Code is easier to learn, read and understand than for machine language.
 Execution faster than high-level languages.
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Disadvantages:
 Programming slower and more tedious than high-level languages. Code is machine specific.

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