Computer Fundamentals MODULE – 1

Basic Computing

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Notes
COMPUTER FUNDAMENTALS

We find computers everywhere around us at home, in schools, hospitals, railway

stations, airports, banks, and shopping malls and so on. Before we proceed with
our study of computers, let us first of all define a computer.
A computer is an electronic machine that takes an input, processes it to produce
the desired output. Every computer is a combination of hardware and software.
The physical components of a computer that can be seen and touched form the
hardware. For example, CPU, monitor, keyboard, printer etc., are hardware or
peripheral devices. The input to a computer is given in the form of instructions.
These set of instructions that we give to the computer to perform a particular task
constitutes a program. Many such programs together form a software for the
computer. Operating system, Antivirus, MS Office, Computer games are all
software applications.

OBJECTIVES
After reading this lesson, you will be able to:
z learn the basic components of a computer along with their functions;
z differentiate input, output and storage devices;
z describe various memory accessing modes;
z explain different ports used to connect various components of a computer;
z classify computers.

1.1 WORKING OF A COMPUTER

To function properly, the computer needs both hardware and software. Hardware
consists of the mechanical and electronic devices, which we can see and touch.
The software consists of programs, the operating system and the data that reside
in the memory and storage devices.

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The working of a computer can be well understood by the block diagram shown
in Fig. 1.1.

CPU

Control Unit
Notes
INPUT Arithmetic and OUTPUT
Logical Unit

Memory unit

Fig. 1.1: Block diagram of a computer

The working of a computer can be broadly categorized into following four

functions or steps.
(i) Receive input – Accept data/information from user through various input
devices like the keyboard, mouse, scanner, etc.
(ii) Process information–Perform arithmetic or logical operations on data/
information.
(iii) Store information—Store the information in storage devices like hard disk,
CD, pen drive etc.
(iv) Produce output–Communicate information to the user through any of the
available output devices like monitor, printer, etc.
The hardware components of the computer specialize in any one of these
functions. Computer hardware falls into two categories: processing hardware and
the peripheral devices. The processing hardware consists of the Central Processing
Unit (CPU), and as its name implies, it is where the data processing is done.
Peripheral devices allow people to interact with the CPU. Together, they make it
possible to use the computer for a variety of tasks.
Now we shall discuss in detail about various components of a computer system.

1.2 COMPONENTS OF A COMPUTER

Computer has four main components
z Input Devices : These are the devices that are used to accept data and
instructions from the user. Keyboard, mouse, scanner etc., are the examples
of input devices.

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z Central Processing Unit (CPU) : This is known as the ‘Brain of the Computer’
as it controls the complete working of the computer.
z Memory: The data and instructions are stored in this component of the
computer. Hard disk, DVD, pen drive etc., are the examples of memory storage
devices.
z Output Devices: These are the devices that are used to display the desired
result or information. Monitor, printer etc., are the examples of output devices.
Notes
Let us now learn each of the components in detail.

1.3 INPUT DEVICES

An input device is used to get data or instructions from the user. This data is then
passed on to CPU for processing so as to produce the desired result. Although
keyboard and mouse are the two common input devices, other devices such as
Optical Character Recognition (OCR), Magnetic Ink Character Recognition
(MICR), and mark sense reader, etc., are also used as per our requirement.

Keyboard
The keyboard is very much like a standard typewriter with a few additional keys.
Generally, we find a QWERTY keyboard with 104 keys on it. The additional keys
may be included in modern multimedia keyboards.

Fig. 1.2: Keyboard

Mouse
The mouse is another very commonly used input device. It is basically a pointing
device that controls the movement of the cursor or pointer on a display screen. It
is a small object that you can roll along a hard and flat surface. As you move the
mouse, the pointer on the display screen moves in
the same direction. A mouse may contain one, two Mouse is an electro-mecha-
or three buttons which have different functions nical device. It is also called
depending on what program is running. as pointing device.

Fig. 1.3: Mouse

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Scanner
Scanner is an input device that can read text or an illustration printed on paper and
translates the information into a form that the computer can use. A scanner works
by digitizing an image - dividing it into a grid of boxes and representing each box
with either a zero or a one, depending on whether the box is filled in. The resulting
matrix of bits, called a bit map, can then be stored in a file, displayed on a screen
Notes and manipulated by programs. Optical scanners do not distinguish text from
illustrations; they represent all images as bit maps. Therefore, you cannot directly
edit text that has been scanned. To edit text read by an optical scanner, you need
an Optical Character Recognition (OCR) system to translate the image into ASCII
characters.

Fig. 1.4: Scanner

Optical Character Recognition (OCR)

An Optical Character Recognition (OCR) is a device that is used for reading text
from paper and translating the images into a form that the computer can
understand. An OCR is used to convert books, magazines and other such printed
information into digital form.

Magnetic Ink Character Recognition (MICR)

An MICR can identify characters printed with a special magnetic ink. This device
particularly finds applications in banking industry. The cheques used for transactions
have a unique MICR code that can be scanned by an MICR device.

Optical Mark Recognition (OMR)

Optical Mark Recognition, also called mark sense reader, is a technology where
an OMR device senses the presence or absence of a mark, such as pencil mark.
OMR is widely used for assessing the objective examinations involving multiple
choice questions.

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Bar Code Reader
A bar code reader is an input device that is generally seen in super markets,
bookshops, libraries etc., A bar-code reader is a photoelectric scanner that reads
the bar codes (vertical striped black and white marks), printed on product
containers. The bar code reader scans the bar code of the product and checks the
description and the latest price of the product.
Notes
Digitizing Tablet
This is an input device that enables you to enter drawings and sketches into a
computer. A digitizing tablet consists of an electronic tablet and a cursor or pen.
A cursor (also called a puck) is similar to a mouse, except that it has a window with
cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen
(also called a stylus) looks like a simple ballpoint pen but uses an electronic head
instead of ink. The tablet contains electronic field that enables it to detect
movement of the cursor or pen and translate the movements into digital signals
that it sends to the computer. Digitizing tablets are also called digitizers, graphic
tablets, touch tablets or simply tablets. Now-a-days most tablets allow you to simply
use your finger to choose items or open or select apps by simply tapping them.

Light Pen
A light pen is an input device that utilizes a light-sensitive detector to select objects
on a display screen.

Speech input devices

Speech or voice input devices convert a person’s speech into digital form. These
input devices, when combined with appropriate software, form voice recognition
systems. These systems enable users to operate microcomputers using voice
commands.

1.4 CENTRAL PROCESSING UNIT (CPU)

As mentioned earlier, CPU is the ‘Brain of your computer’. This is because it
processes or executes the instructions given to the computer. Any type of
instruction given to the computer using any of the input devices has to be sent to
the CPU for execution. In a microcomputer, the CPU is based on a single chip
called the microprocessor.
A typical CPU has the following components:
z Control Unit (CU)
z Arithmetic Logic Unit (ALU)
z Memory Registers

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1.4.1 Control Unit (CU)
The Control unit manages the instructions given to the computer. It coordinates
the activities of all the other units in the system by instructing rest of the
components of the computer about how to carry out a program’s instructions. It
reads and interprets instructions from memory and transforms them in to series of
signals to be executed or stored. It also directs the movement of these electronic
Notes signals between memory and ALU or between CPU and input/output devices.
Hence it controls the transfer of data and information between various units. The
user’s program provides the basic control instructions. Conceptually, the control
unit fetches instructions from the memory, decodes them and directs the various
units to perform the specified functions.

1.4.2 Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit or ALU performs two types of operations - arithmetic and
logical. Arithmetic operations are the fundamental mathematical operations
consisting of addition, subtraction, multiplication and shifting operations. Logical
operations consist of boolean comparisons such as AND, OR and NOT.

1.4.3 Memory Registers

The CPU processes data and instruction with high speed. There is also movement
of data between various units of the computer. It is necessary to transfer the
processed data with high speed. So the computer uses a number of special
memory units called registers. A memory register is a sort of special storage area
that holds the data and instructions temporarily during processing. Since this is
internally located in the CPU, the processing time is very less. They often hold
data for less than a millisecond. This high speed storage area make processing
more efficient.

To locate the characters of data or instructions in the main memory, the computer
stores them in locations known as addresses. A unique number designates each
address. Addresses can be compared to post office mailboxes. Their numbers
remain the same, but contents continuously change.

The contents of the memory are held only temporarily, that is, it is stored only as
long as the microcomputer is turned on. When you turn the machine off, the
contents are lost. The capacity of the memory to hold data and program
instructions varies in different computers. The original IBM PC could hold
approximately several thousand characters of data or instructions only. But
modern microcomputers can hold millions or even billions of characters in their
memory.

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How the CPU and Memory work together?
The working of the CPU and memory is shown in Fig. 1.5.

Control Unit Arithmetic-Logic Unit

Notes

Programs Data

Enter 1st Enter 2nd

100 4
Number Number

Multiply Print the

400 400
1st and 2nd result

End

Output

Input

Fig. 1.5: Working of the CPU and Memory

Various steps involved for multiplying two numbers is shown in Fig. 1.5. Let us
take an example and understand how CPU and memory work together to execute
a given instruction. The control unit recognizes that the program has been loaded
into the memory. It begins to execute the first step in the program.
1. The program tells the user, “Enter 1st Number”.
2. The user types the number 100 on the keyboard. An electronic signal is sent
to the CPU.
3. The control unit recognizes this signal and routes the signal to an address in
memory - say address 7.
4. After completing the above instruction, the next instruction tells the user,
“Enter 2nd Number.”
5. The user types the number 4 on the keyboard. An electronic signal is sent to
the CPU.

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6. The control unit recognizes this signal and routes it to memory address 8.
7. The next program instruction is executed - “Multiply 1st and 2nd Numbers”.
8. To execute this instruction, the control unit informs the ALU that two
numbers are coming and the ALU has to multiply them. The control unit
next sends to the ALU a copy of the contents of address 7 (100) and address
8(4).
Notes 9. ALU performs the multiplication: 100 × 4 = 400
10. The control unit sends a copy of the multiplied result (400:) back to memory
to store it in address 9.
11. The next program instruction is executed: “Print the Result.”
12. To execute this instruction, the control unit sends the contents of the address
9 (400) to the monitor.
13. Monitor displays the value 400.
14. Final instruction is executed: “End”. The program is end.
Please note that Fig. 1.5 is a simplified version of the actual processing activity.
The actual working of the CPU and memory is much more complicated. For
example, there are actually many more memory addresses - thousands to millions
that cannot be shown here. Moreover, the addresses are in a form that the
computer can interpret. The data and instructions are stored in the computer in the
form of 0s and 1s only.

1.5 OUTPUT DEVICES

Output devices receive information from the CPU and present it to the user in the
desired form. Some of the output devices are monitor, printers, plotters, etc. Let
us now learn each of them in detail.

1.5.1 Monitor
The monitor is just like a television screen and it is used to display data and
information. When some data or instruction is being keyed in, the monitor displays
the characters being typed. The monitors are
available in various sizes. They may also differ for Monitor is also called as
different types of computers. The standard size is Visual Display Unit
24 lines by 80 characters. The output displayed
on the monitor is called soft copy.
There are two types of monitors – CRT and TFT-LCD monitors.
CRT Monitor : CRT (Cathode Ray Tube) monitor is a relatively older type of
monitor. It is rarely being used today. These were bigger and bulkier monitors and
hence took lot of desk space. They also consumed lot of electricity.

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TFT-LCD monitors: TFT stands for Thin Film Transistor and LCD stands for
Liquid Crystal Display. These monitors are lighter and occupy less space. They are
also commonly referred to as flat screen displays and consume much less
electricity than CRT monitors. Now-a-days even LED (Light Emitting Diode)
monitors are being used.

Notes

Fig. 1.6: monitor

1.5.2 Printer
You must have used printer for taking printouts. Printer is a device that produces
the output on paper. Such an output is also known as hard copy and it may be in
the form of text or graphics. There are many different types of printers. These
printers vary in terms of size, speed and quality of output. Some of them are
discussed below:
(i) Dot Matrix Printer : It is a type of printer that uses a print head to print
characters on paper. The print head moves in back and forth or up and
down motion on the page. The print head strikes on an ink soaked cloth
ribbon that is laid against a paper. The characters formed from dots are thus
printed on the paper.
(ii) Ink-jet Printer: Ink-jet printers work by spraying ionized ink on a sheet of
paper. Magnetized plates in the ink’s path direct the ink onto the paper in
the desired shapes. Ink-jet printers are capable of producing a better print
than the dot matrix printers. A typical ink-jet
printer provides a resolution of 300 dots per
inch, although some newer models offer higher
resolutions. These are also known as Line
printers as the output is produced line by line.
In general, the price of ink-jet printers is lower
than that of laser printers. However, they are
also considerably slower. Another drawback of
ink-jet printers is that they require a special type
of ink that is apt to smudge on inexpensive Fig. 1.7: Ink-jet printer

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copier paper. Since ink-jet printers require smaller mechanical parts than
laser printers, they are especially popular as portable printers. In addition,
colour ink-jet printers provide an inexpensive way to print full-colour
documents.
(iii) Laser Printer: It works on the principle of a photocopier. It utilizes a laser
beam to produce an image on a drum. The light of the laser alters the electrical
Notes charge on the drum wherever it hits. The drum is then rolled through a
reservoir of toner, which is picked up by the charged portions of the drum.
Finally, the toner is transferred to the paper through a combination of heat
and pressure.
Since the entire page is transmitted to a drum before the toner is applied,
laser printers are sometimes called page printers. In addition to text, laser
printers are very adept at printing graphics. However, you need significant
amounts of memory in the printer to print high-resolution graphics.
The speed of laser printers ranges from about 4 to 20 pages of text per
minute (ppm). A typical rate of 6 ppm is equivalent to about 40 characters
per second (cps).
(iv) Thermal printer: Thermal printers are printers that produce images by
pushing electrically heated pins against special heat-sensitive paper. Thermal
printers are inexpensive and are used in most calculators and many fax
machines. They produce low-quality print, and the paper tends to curl and
fade after a few weeks or months.

1.5.3 Plotter
A Plotter is a device that is used to draw charts, graphs, maps etc., with two or
more automated pens. Multi-colour plotters use different-coloured pens to
produce a multi-coloured output.

Fig. 1.8: Plotter

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Different types of plotters are available in the market. A drum plotter has a paper
wrapped around a moving drum and the pens move on the paper to print the
output. A flatbed plotter has a flat surface on which the paper is placed and the
pens move to draw the output. An electrostatic plotter has a negatively charged
paper on which the drawing is made using a positively charged toner.
Plotters are considerably more expensive than printers. These were the first of the
devices that could print full sized engineering drawings with colour. They are Notes
frequently used for Computer Aided Engineering (CAE) applications such as
Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM).

1.5.4 Speakers
The speakers are used to produce audio output. The computers have sound cards
that enable the computer to produce audio output through the speakers.

Fig. 1.9: Sound Card and Speakers

Now-a-days, 3D audio is a technique for giving more depth to traditional stereo

sound. Typically 3D sound or 3D audio is produced by placing a device in a room
with stereo speakers. The device dynamically analyses the sound coming from the
speakers and sends feedback to the sound system so that it can read just the sound
to give the impression that the speakers are further apart. 3D audio devices are
particularly popular for improving computer audio where the speakers tend to be
small and close together. There are a number of 3D audio devices that can be
attached to a computer’s sound card.

INTEXT QUESTIONS 1.1

Fill in the blanks:
1. The four basic functions performed by the computer are ..................,
.................., .................., ..................
2. A bar code reader is a / an .................. device.

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3. Choose the correct answer:
(a) Arithmetic and logical operations is performed by ................... unit.
(i) ALU (ii) Editor (iii) storage (iv) output
(b) The ALU and CU are jointly known as ..................

Notes (i) RAM (ii) ROM (iii) CPU (iv) none of the above
(c) The process of producing results from the data for getting useful
information is called as ..................
(i) output (ii) input (iii) processing (iv) storage

1.6 MEMORY UNIT

There are two kinds of computer memory: primary and secondary. Primary
memory is accessible directly by the Central Processing Unit. RAM is an example
of primary memory. You will know more about RAM later in this lesson. As soon
as the computer is switched off, the primary memory loses its contents. But data
can be stored and retrieved at much faster rate with primary memory as compared
to secondary memory. Examples of secondary memory storage devices are floppy
disk, magnetic disk, hard disk, CD, pen drive etc. The secondary memory devices
may be inside or located outside the computer. Primary memory is more expensive
than secondary memory.
When the computer is doing any task, the data that have to be processed are stored
in the primary memory. This data may come from an input device like keyboard or
from a secondary storage device like a hard disk. As program or the set of
instructions is kept in primary memory, the computer is able to follow them
instantly. For example, when you book ticket from railway reservation counter,
the computer has to follow some steps, viz., take the request, check the availability
of seats, calculate fare, wait for money to be paid, save the reservation and print
the ticket. The program containing these steps is kept in primary memory of the
computer.
But inside the computer, the steps followed are quite different from what we see
on the monitor or screen. In computer’s memory both programs and data are
stored in the binary form. You have already been introduced with decimal number
system that is the numbers 0 to 9. The binary system has only two digits, 0 and 1.
These are called bits. A bit is an acronym for binary digit, which stands for one
binary piece of information. As human beings we all understand decimal system
but the computer can only understand binary system. Consider that a computer
consists of numerous switches. If a switch is ON then it is considered as 1
otherwise it is considered as 0. A number of switches in different states will give
you a message like this: 110101......10. So the computer takes input in the form of
0 and 1 and gives output in the same form, i.e., 0 and 1 only. But we do not receive

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output in the form of 0’s & 1’s only. This is because every number stored in binary
form can be converted to decimal system and vice versa. For example, 1010 in
binary is equivalent to 10 in decimal. Therefore, it is the computer that takes
information or data in decimal form from you, converts it into binary form,
processes it, produces output in binary form and finally again converts the output
to decimal form.

Measuring Memory Notes

The primary or internal storage unit is made up of several small storage locations
called cells. Each of these cells can store a fixed number of bits called word length.
Each cell has a unique number assigned to it called the address of the cell and it is
used to identify the cells. Hence we can say that memory is like a large cabinet
containing as many drawers as there are addresses on memory. Each drawer
contains a word and the address is written on outside of the drawer.

You know that data in computer is stored in the form of 0s and 1s. Each of these
digits is known as a bit. A collection of 8 bits constitutes a byte. Each cell of
memory contains one character or 1 byte of data. So the capacity is defined in
terms of bytes or words. However higher units of memory are Kilobytes,
Megabytes, Gigabytes etc. 1 Kilobyte is equal to 1024 bytes. Thus 64 Kilobyte
(KB) memory is capable of storing 64 × 1024 = 32,768 bytes. Other units of
memory are listed in the table below:

(KB) Kilobyte 210 = 1024 bytes

(MB) Megabyte 220 = 1024 KB
(GB) Gigabyte 230 = 1024 MB
(TB) Terabyte 240 = 1024 GB

1.6.1 Primary Memory

Primary memory is the memory that is accessed by the processor directly. It is also
known as main memory or internal memory. It helps in executing applications that
are temporarily stored in a specific memory location. Primary memory is of two
types – RAM and ROM.

Random Access Memory (RAM)

Random Access Memory (RAM) is the type of memory in which it is possible to
randomly select and use any location of the memory directly to store and retrieve
data. It is also called as read/write memory. Since it is volatile, the data from RAM
is lost as soon as the power to the computer is switched off.

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Read Only Memory (ROM)
This is another type of primary memory from which data can only be read. We
cannot write or modify data once written on to the ROM. Also this type of primary
memory is not volatile. The storage of program and data in the ROM is permanent.
The ROM stores some standard processing programs supplied by the manufacturers
to operate our computer. The Basic Input Output System (BIOS) is stored in the
Notes ROM. It examines and initializes the start up process of the computer and also
checks various peripheral devices attached to the PC when the computer is turned
ON. The various types of ROMs are discussed below:
z Programmable Read Only Memory (PROM): You know that it is not
possible to modify or erase programs stored in ROM, but it is possible for
you to store your program in PROM chip. Once the programs are written it
cannot be changed. Also the program is not lost even if power is switched off.
z Erasable Programmable Read Only Memory (EPROM) : This type of
ROM overcomes the problem of PROM and ROM. EPROM chip can be
programmed time and again by erasing the information stored earlier in it.
Information stored in EPROM can be erased by exposing it to ultraviolet
light. This memory can be reprogrammed using a special programming facility.
When the EPROM is in use, information can only be read.
z Electrically Erasable Programmable Read Only Memory
(EEPROM):This type of ROM is somewhat similar to EPROM. The only
difference is that unlike EPROM, electrical signals are used to erase the
contents of EEPROM. Also, this type of ROM need not be completely erased.
Partial modification of ROM is possible.

1.6.2 Cache Memory

The speed of CPU is extremely high as compared to the access time of main
memory. Therefore, the performance of CPU decreases due to the slow speed of
main memory. To increase the performance of CPU, a small memory chip is
attached between CPU and main memory whose access time is very close to the
processing speed of CPU. This memory is called as Cache memory. Cache
memories are accessed much faster than conventional RAM. It is used to store
programs or data currently being executed or data that is being frequently used by
the CPU. Fast access of these data and instructions increases the overall execution
speed of the software. It is very expensive memory and so has to be used in a
limited amount.
Cache memory is also known as CPU memory. It is either integrated directly with
the CPU chip or is placed separately on the motherboard. As the microprocessor
processes data, it first looks in the cache memory. If the required data or
instructions are found there, it does not have to spend more time in reading data

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from other storage devices that have slower access time. Hence the processing
speed increases.

1.6.3 Secondary Memory

You are now clear that the operating speed of primary memory or main memory
should be as fast as possible so as to cope up with the CPU speed. These high-
speed storage devices are very expensive and hence the cost per bit of storage is Notes
also very high. Again, the storage capacity of the main memory is also very limited.
Often it is necessary to store hundreds of millions of bytes of data for the CPU to
process. Therefore, additional memory is required in all the computer systems.
This memory is called auxiliary memory or secondary storage.
In this type of memory the cost per bit of storage is low. However, the operating
speed is slower than that of the primary memory. Huge volume of data are stored
here on permanent basis and transferred to the primary storage as and when
required. Most widely used secondary storage devices are hard disks, CDs, DVDs
and pen drives. But before learning about these modern storage devices let us also
have a look at some primitive storage devices like magnetic tapes, magnetic
drums and floppy disks.

Magnetic Tape
Magnetic tapes are used for large computers like mainframe computers where
large volume of data is stored for a longer time. Earlier these were used with PCs
also. The cost of storing data in tapes is inexpensive. Tapes consist of magnetic
materials that store data permanently. It can be 12.5 mm to 25 mm wide plastic
film-type and 500 meter to 1200 meter long which is coated with magnetic
material. The deck is connected to the central processor and information is fed
into or read from the tape through the processor. It is similar to a cassette tape
recorder.

Fig. 1.10: Magnetic Tape

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Magnetic Disk
You might have seen the gramophone record, which is circular like a disk and
coated with magnetic material. Magnetic disks used in computer are also made on
the same principle. It rotates with very high speed inside the disk drive. Data are
stored on both the surfaces of the disk. Magnetic disks are most popular for direct
access storage. Each disk consists of a number of invisible concentric circles
Notes called tracks. Information is recorded on tracks of a disk surface in the form of tiny
magnetic spots. The presence of a magnetic spot represents one bit (1) and its
absence represents zero bit (0). The information stored in a disk can be read many
times without affecting the stored data. So the reading operation is non-destructive.
But if you want to write a new data, then the existing data is erased from the disk
and new data is recorded.

Floppy Disk
It is similar to magnetic disk discussed above. It is 3.5 inch in diameter. The
capacity of a 3.5 inch floppy is 1.44
Floppy disks have been made obsolete
mega bytes. It is cheaper than any other
because the storage space was very
storage devices and is portable. The
small in floppy disks in comparison to
floppy is a low cost device particularly
other storage devices.
suitable for personal computer system.

Fig. 1.11: Floppy Diskette

Hard Disk
A hard disk is the most commonly used secondary storage device. Although
generally it is fixed inside the CPU cabinet but still external hard disks are also
available. It can store huge amount of data and also and provides relatively quick
access to data stored on it.
A hard disk is a set of numerous disks stacked one above the other with a
cylindrical spindle in-between (Fig. 1.12). The data is recorded electromagnetically
in the form of concentric circles called tracks. The tracks are further divided into
blocks as shown in the figure. In the hard disk drive, there is a Read/Write head
mounted on the arm placed next to the stacked disks. This head moves horizontally
and vertically to read or write data on the disks.

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Read/write head Arm
Spindle

Block

Cylinder
Notes

Track

Sector

(a) A hard disc drive (b) A single disk

Fig. 1.12: Hard disk

Optical Disk
With every application and software there is greater demand for memory capacity.
It is the necessity to store large volume of data that has led to the development of
optical disk storage medium. Optical disks can be divided into the following
categories.
z Compact Disk - Read Only Memory (CD-ROM): CD-ROMs are made of
reflective metals. A CD-ROM is written during the process of manufacturing
by high power laser beam. Here the storage density is very high, storage cost
is very low and access time is relatively fast. Each disk is approximately 4 ½
inches in diameter and can hold over 600 MB of data. As the CD-ROM can
be read only we cannot write or make changes into the data contained in it.
z Compact Disk - Recordable (CD-R) : These CDs can be used to write data
on to them provided your computer has a CD writer. The CD writer uses a
special laser light to write data on to a blank CD. Once the CD-R has been
burnt, i.e. data has been written on it, it cannot be modified. The information
can be added to it but the parts that have been burnt cannot be edited.
z Compact Disk – Read/Write (CD- R/W): This type of CD can be used for
both reading and writing. Also these can be written and erased again and
again.
z Digital Versatile Disk (DVD) : A DVD is an optical storage disk with much
larger storage capacity than that of CDs. A single sided DVD can store upto
4.7 GB of data. Due to its high storage capacity, DVDs are generally used to
store movies and other audio video files.

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Flash Memories
Flash memory is a memory chip that is used for storage and also for transferring
of data between a computer and digital device. A flash memory is one that retains
data in spite of the electricity supply being switched off. Hence it is a non- volatile
memory. It evolved from EPROM and EEPROM but more often it is said to be a
distinct type of EEPROM which is programmed and erased in blocks. That means
Notes devices using flash memories erase data at the block level. A block of flash
memory chip must be erased before data is written on it.
Flash memory is widely used for storage in consumer devices like mobile phones,
USB flash drives, tablet computers, digital cameras and other solid state drives. It
is the least expensive form of semiconductor memory. It is non-volatile and
consumes very less power. That is why its use is increasing day by day, especially
for in-memory devices to help speed up performance and at the same time increase
the scalability of the devices. The data in flash memory can be erased, modified
and rewritten many times. It does not require batteries for solid state storage. It
has very fast access time and also has higher resistance to kinetic shock as
compared to hard disk drive. It is extremely durable and can withstand extreme
pressure and temperature.
The memory card that you find in your digital cameras and mobile phones is also
a type of flash memory. A variety of such cards are available in the market. Some
of the varieties are Secure Digital Card (SD Card), Memory stick, Multimedia
Card (MMC) etc. The price of these cards depends on their size and their storage
capacities.
Another form of flash memory or solid state memory is a pen drive. A pen drive
is a small portable secondary storage device (somewhat shaped like a pen) that
connects to a computer through a USB port. It functions as a portable hard drive
and is small enough to be carried easily. These are also known as thumb drives.

INTEXT QUESTIONS 1.2

1. Fill in the blanks.
(a) 1 KB = .................... bytes.
(b) Primary memory is of two types : .................... and ....................
(c) To increase the performance of CPU, a small memory chip is attached
between CPU and main memory whose access time is very close to
the processing speed of CPU. This memory is called ....................
memory.
(d) A hard disk is the most commonly used .................... storage device.

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2. State whether the following statements are true or flase:
(a) There are two kinds of computer memory: primary and secondary.
(b) The computer can understand decimal system also.
(c) The storage of program and data in the RAM is permanent.
(d) PROM is secondary memory.
(e) The memories which do not lose their content on failure of power Notes
supply are known as non-volatile memories.

1.7 MEMORY ACCESSING MODES

An addressing mode refers to the manner in which a given memory location is
accessed. Some of the memory accessing modes are discussed below:

1.7.1 Direct Access or Random Access

It is the type of accessing mode in which the value to be stored in a particular
memory location is obtained directly. Since the data can be accessed in any order
that is why this type of memory access is also known as random access of memory.
This type of memory access is generally fast and more flexible. The type to be
stored in memory is obtained directly by retrieving it from another memory
location. This type of memory access is based on the principle that any piece of
data can be returned in a constant time, regardless of its physical location and
previous access. The web uses direct memory access mode.

1.7.2 Sequential Access memory

It is the type of memory in which the stored data is read in sequence. That means
if you want to display the fourth record, the reading will start from the first record
and then move to second, third and then fourth record. This type of memory
access can be time consuming and hence slow, especially when the data to be read
is towards the end. Sequential access devices are generally a form of magnetic
storage. Hard disks, CD-ROMs and magnetic tapes use sequential access of
memory.
The Fig 1.13 illustrates the concept of random and sequential memory access.
Sequential access

1 2 3 4 5 6 7 8
Random access

1 3 7 2 8 6 4 5
Fig. 1.13: Sequential and Random Memory Access

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1.8 SYSTEM SECURITY AND DATA SECURITY
Securing your computer and also the data stored on your computer is the
worldwide concern today. Securing stored data involves preventing unauthorized
people from accessing it. It also includes preventing accidental or even intentional
destruction or modification of data. Hence data security involves digital privacy
Notes measures that are applied to prevent any sort of unauthorized access to computers,
databases or even websites.
There are various data security measures that are prevalent nowadays. These
include software/hardware disk encryption, backups, data masking, scrambling
etc.

1.9 PORTS
Ports are the connecting points on the CPU. Monitor, keyboard, printer and other
peripheral devices are connected to the computer through ports. Some of the
ports are discussed below:

Serial Ports
A serial port transfers data one bit at a time. It is a single wire that transmits 8 bits
of data. Also a start byte has to be transmitted before each byte of data and a stop
bit has to be sent after the byte. Serial ports are also known as COM ports or
RS232C ports and come in the form of 9 pin or 25 pin male connector. A mouse
is connected to the CPU through a serial port.

Parallel Port
A parallel port sends or receives 8 bits (1 byte) at a time. These 8 bits are
transmitted in parallel to each other. These ports come in the form of 25-pin
female connector and are generally used to connect devices like printer, scanner,
external hard disk drive etc.

USB Port
USB stands for Universal Serial Bus. It is becoming popular day by day and is used
to connect variety of devices like printers, scanners, mouse, keyboard, speakers
etc. It is a simple and an easy to use port.

InfraRed Port
This port sends and receives a ray of light of infrared frequency from one device
to another. These types of ports are used for wireless data transmission. This is the
same technology that is used for TV remotes and in case of computers, it is used
in devices like wireless keyboard and wireless mouse.

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Bluetooth
A Bluetooth is a telecommunication industry specification that is used to connect
mobile phones, computers and other such devices to connect to each other using
short range wireless connection. The maximum range of Bluetooth communication
is 10 meters.

1.10 CLASSIFICATION OF COMPUTERS Notes

The computers can be classified according to their shapes and sizes and also
according to the technology being used. Do you know the different types of
computers available in the market today?
Broadly, computers can be of three types:
z Analog Computers: These computers work with continuous and physical
quantities like temperature, voltage, current, weight etc. These are not as
accurate as digital computers. They are used in engineering and scientific
applications. For example, a blood pressure monitoring machine is a type of
analog computer.
z Digital Computers: These computers work with discrete quantities. The
data is converted into binary form i.e., 0s and 1s.These are much faster than
the analog computers and are also far more accurate. We use digital computers
for scientific and business applications. Digitally programmed watches are
good examples of digital computers.
z Hybrid Computers: These types of computers use both analog and digital
technology. Some calculations may take place in analog manner while others
may be in digital form. These are used in weather forecasting.

1.10.1 Types of Digital Computers

Digital computers can be further classified as follows:
(i) MicroComputers
A microcomputer is a computer that contains a microprocessor chip inside
it. These are mainly used in offices, homes, schools, shops etc. These
microcomputers can be further categorized as :
a. Mobile Computers: These computers can be held in hand and used for
variety of purposes. Although they have limited capabilities as compared
to other micro- computers, yet they are being used extensively, these
days because of excellent features contained in them. An excellent
example of this type of microcomputer is a smartphone. In addition to
communicating with people, a smartphone has an internet connection

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so that we use various web services like email, chat, video chat, GPS,
online games etc. Smartphones generally have a touch screen interface.
b. Portable Personal Computers: This category of microcomputers
includes laptops, notebooks, tablets etc. These are larger in size than
mobile computers but can be easily carried from one place to another.
c. Desktop PCs: These computers are installed on a table or desk. These
Notes
are large and heavy computers. So they are not portable. These are
generally used in places where the user has to work sitting at one
place only like offices, shops, hospitals, ticket booking counters etc.
(ii) Minicomputers
Minicomputers provide faster operating speeds and larger storage capacity
than microcomputers. These serve as servers in multiuser environments.
These computer can support large number of high speed input/output devices
and also many users can simultaneously work on these systems. Small
business organizations having about 50-100 users use minicomputers as
their servers.
(iii) Mainframe Computers
Mainframe computers or simply mainframes are the second largest in terms
of the capacity and size of computers. Mainframes are huge and very
expensive computers but can support hundreds of users at a time. These
multi-processor systems have very large storage capacity and so can handle
huge volumes of data and information. These are used in large organizations
like railways where centralized data for the entire railway reservation system
is maintained.
(iv) Supercomputers
Supercomputers are the most powerful computers in the world. In a
supercomputer many processors work simultaneously, so they have very
high processing speed. They can process huge volume data and information
with ultrafast calculations. Supercomputers are used in specialized
applications like weather forecast, space research, molecular modeling etc.

INTEXT QUESTIONS 1.3

Fill in the blanks:
1. USB stands for ..................
2. The maximum range of bluetooth communication is .................. meters.
3. Digital computers can be classified as .................., .................., ..................
and ..................

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WHAT YOU HAVE LEARNT

z Computer is an electronic machine that takes an input, processes it to produce
the desired output.
z Hardware consists of the mechanical and electronic devices, which we can
see and touch. Notes
z The software consists of programs, the operating system and the data that
reside in the memory and storage devices.
z Computer has four main components namely input devices, output devices,
memory, CPU.
z An input device is used to get data or instructions from the user.
z Central Processing Unit is the brain of computer.
z Output devices receive information from the CPU and present it to the user
in the desired form.
z There are two kinds of computer memory: primary and secondary.
z Direct access memory is the type of accessing mode in which the value to be
stored in a particular memory location is obtained directly.
z Sequential access memory is the type of memory in which the stored data is
read in sequence.

TERMINAL EXERCISE
1. What are the major components of a computer?
2. What is CPU and how does it work? Explain briefly.
3. What is a plotter and how does it work?
4. Describe the various types of printers briefly.
5. Differentiate between the following:
(a) RAM and ROM
(b) Volatile and non-volatile memory.
(c) Sequential access and Random access
6. Explain different types of ports.

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ANSWERS TO INTEXT QUESTIONS

1.1
1. receive input
Notes process information
produce output
store information for future use
2. input
3. (a) ALU (b) CPU (c) processing

1.2
1. (a) 1024
(b) RAM, ROM
(c ) cache
(d) secondary
2. (a) True (b) False (c) False
(d) False (e) True

1.3
1. Universal Serial Bus
2. 10
3. Microcomputers, minicomputers, mainframe computers, supercomputers.

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