1

Chapter Four
Introduction to Computer System
Computer is a data processing machine which consists of several integrated components that
works together as a single unit to achieve some objective. The computer system refers to the
computer itself and all other components interconnected to it. A computer system components
are classifies into hardware and software which cooperates to provide full system functions of
the computer.

1. The Computer Hardware

The Hardware is the physical (visible and tangible) part of the Computer that you can see and
touch. It includes electronic devices, which have the potential for performing the task of solving
problems. It is the general term for the physical machines or devices that carry out the
activities of capturing, processing, storing and communicating data and information. The
computer hardware is divided into the following categories:
A. Input Devices C. Output Devices
B. Central Processing Unit D. Storage Devices& others
CPU

Control Unit
Input Devices Output Devices
Memory (register)

 Keyboard ALU  Monitor

 Mouse  Printer
 Scanner Secondary Storage  Speaker
 Microphones  Disk drives
Devices
 Disk drives  plotter

Fig. 1 Basic Units of a computer System

1
 2

A. Input Devices
Input devices are devices through which data or information is entered into the computer. It is
used to convert human readable form to machine-readable form. There are different input
devices like: Keyboard, mouse, Image Scanner, Disk drives, microphone, touch screen, light pen,
magnetic ink character recognition (MICR), bar code reader, camera systems, etc.
 Keyboard: The keyboard is an input device used to enter information into your PC.

The keys on the keyboard can be divided into 5 sections.

o Alphanumeric (Character Keys): These keys work just like a conventional type writer
which consists of letters (A-Z), numbers (0-9), Enter key, Spacebar, Backspace, Shift,
Caps lock, etc.
o Function Keys: labeled from F1 to F12.
o Numeric Keys: Let you enter numerical data more easily when you are working on
numbers. To use this section of the keyboard, make sure that the Num Lock key is ON.
o Navigation (Cursor movement Keys): These keys are used to navigate through your
document. The keys are: Arrow keys, Home, End, Page up, Page down, etc.
o Computer (Special) keys: They perform different tasks when used alone or in
conjunction with other keys. Some of these keys are: Alt, Ctrl, Print Screen, Scroll Lock,
Pause, Delete, and Insert.
 Mouse: The mouse is a pointing device that is used to move the insertion pointer
around the screen. It has two buttons left (primary) button and right button. Through
which you can operate different operations. Such operations are:
 point: indicate the item
 click: press and release the primary key
 right click: press and release on right key
 double-click: press twice on left key
 drag: press the left key and move

2
 3

 Scanner: which is an input device used to input data into a computer. It converts the
data from hard copy to soft copy. Once the data is transferred to the computer,
through the scanner, it can be modified, or combined with other information.
 Disk drives: Are data read/write devices used to input data into the computer. E.g.
floppy drive, CD-R, CD-RW and DVD drive.
 Microphones: It captures sounds and translates into digital signals for the computer.
 Touch screen: it is touch sensitive transparent panel covering the screen.
 Light pen: that utilizes the light sensitive detector to select objects on a display
screen.
 Magnetic ink character recognition (MICR): allows the computer to recognize
characters printed using magnetic ink. Example of this device is card reader in the bank.
 Bar code reader: is a photoelectric scanner that read the bar codes, or vertical zebra
striped marks, printed on product containers.
 camera systems: used to input images and sounds in to the computer e.g. digital
camera
B. Central Processing Unit (CPU)
It is the most costly and main component of the computer. It may be a single chip or a series of
chips that performs arithmetic and logical operations and controls the operation of the other
elements of the system. CPU follows the instruction of the software to manipulate data into
information. It executes program instructions and performs the computer’s processing
activities. The CPU is called brain of computer and also called the microprocessor.
The CPU mostly performs the two major functions.
1. Performing arithmetic and logical operations and
2. Controlling every activity of the computer like:
a. Controlling internal and external devices
b. Controlling memory usage for storing data and instructions.
c. Controlling sequence of instructions
Purpose of CPU

 Fetch instruction: The CPU read instruction from the memory

3
 4

 Interpret instruction: the instruction must be decoded to determine what action is required
 Fetch data: the execution of an instruction may require reading of data from memory or an
I/O module.
 Process data: the execution of an instruction may require performing some arithmetic or
logical operation on data.
 Write data: The result of an execution may require writing data to memory or an I/O
module.
The CPU has three major components which connected by cables called bus to communicate
each other:
Control Memory
unit (register)
ALU
Figure 4.1. The components of CPU

The Control Unit: Controls every activity of the computer. The control unit ensures that
according to the stored instructions, the right operation is done on the right data at the
right time.
 All computer activities are carried out according to instructions that the control unit
receives.
 Fetches and store data and instruction from memory to register and vice versa.
 Receives an instruction, decodes/interprets and passes it to the ALU for execute.
 Determines the next instruction to execute.
 Tells the rest of the computer system how to carry out the program’s instructions.
 Directs the movement of electronic signals between:
 Main memory and the ALU
 Main memory and the I/O devices
The Arithmetic or Logic Unit (ALU): Contains the electronic circuitry that performs the
arithmetic operations and logical operations, that underline all computing capabilities and
controls the speed of those operations.
 Arithmetic unit performs actual computing and calculations based on fundamental

4
 5

mathematical operations: like (+, -, *, /)

 Logical unit: - based on the instruction provided to it, perform logical comparison
between data items. The comparison determines whether the information is greater
than, less than or equal to the other information by using Logical operations like (>, <,
<=, >=, =).
The memory (register): The CPU needs a small internal memory called registers used to
store intermediary results from the operation of ALU.
- To temporarily store some data
- To remember the location of the last instruction
- To store instruction and data temporarily while execution
in other words,
- This storage has very fast access time low storing capacity.

C. Output Devices
The output devices enable the user to see the information on the computer. It converts the
results of a process, which is only in machine understandable to a human understandable form.
Included in the output devices are:
I. Visual Display Unit (VDU) or Monitor: Sometimes also called screen, displays the output
of the processing activity for the user on a television-like screen. VDU can be either Liquid
Crystal Display (LCD) or Cathode Ray Tube (CRT). Video displays differ in:
 Size:
 Resolution:
 Colors:
 Monochrome: means one color, generally white on black background or
vice versa.
 Color Monitors: Many monitors display color-combining shades of red,
green, and blue (RGB).
II. Printer: Printers are most widely used output devices. It produces hard copy materials
that are paper output. Different types of printers are in use today. In general, there are
two major categories of printers. Namely:

5
 6

 Impact Printers
 Non-Impact printers.
 Impact Printers: in impact printing, the paper and the character being
printed come in contact with one another. That is, striking an inked ribbon
with pins forms characters. Examples of Impact Printers are: Dot Matrix, Line
and Character printers.
 Non-Impact Printers: are printers that do not bring the paper and the print
material into physical contact. The characters of the print material are
produced on the paper through a heat, chemical, or spraying process. Laser
and Ink-Jet Printers are the most frequently used kinds of Non-Impact
printers.
III. Disk drives: since they are also used to record a result of a process on magnetic disks,
they are also considered as output device.
IV. Modem: links two or more computers by translating digital signals into analog signals so
that data can be transmitted via telecommunications. Modem can be either internal or
external modem. Internal modem is a hardware fitted into an expansion slot in the system
unit. External modem sits outside your system and connects to serial port.
V. Plotters: specialized output device designed to produce high quality graphics in a variety
of colors. It used for creating large hard copy items, such as maps, architectural drawings,
3D illustrations items typically too large for regular printers
VI. Speaker: this is a device specially used to provide audio output.
D. Storage Devices
Storage device is used to store data or information internally or externally. Storage device can
classify into primary (main memory) and secondary storage device.
Primary (main memory): It is a means of storage that is found within the computer itself
and that is why it is called internal memory or primary memory.
 Have low capacity
 High speed and
Primary memory includes RAM and ROM.

6
 7

RAM: is a random access memory (can be accessed randomly without regard to any other
memory location. It is working area of the computer.
 It is volatile it holds data as long as there is current flow.
 It allows read/write
 Holds data temporarily.
 Expensive
ROM: Stands for read only memory. Once programmed, it can only be read from it.
 It is nonvolatile: unlike RAM, the contents cannot be changed or lost when
electric current is turned off. It stores data permanently.
 It is read only memory: we cannot write or change the contents of ROM.
Secondary storage device: it also called Secondary memories or Mass Storage devices. It
used for mass storage of programs and data files. Because of the primary storage doesn’t
store user’s data permanently, their high price and limited capacity, the need to have other
type of storage to hold large amount of data for a longer period of time in a less expensive
and yet accessible manner is evident.
 Have the capability to store large amount of data for a longer period of time.
 It is reading a writing device.
 Inexpensive compared to primary storage.
There are two types of secondary storage: Magnetic Storage and Optical storage.
A. Magnetic Storage: Is storage devices made up of Iron Oxide particles mixed with a
binding agent. They use magnetic technology to read and write data and
information from and to the surface of storage area. The most common types of
secondary storage are: Magnetic tape and Magnetic disk
I. Magnetic Tape: is the earliest form of secondary storage. Data can be stored on
and retrieved from tape sequentially. Magnetic tape is not so widely used for file
processing, but still plays an important part in the file back up for security
purposes.
II. Magnetic disk: are flexible plastic or metal (rigid aluminum) disks of easily
magnet able materials. There are two types of magnetic disks on which we can

7
 8

store and retrieve randomly.

 Hard disk: is a high capacity magnetic disk, which is fixed in the main unit of the
computer. Hard disks cannot be removed from their disk-drive cabinets, which
contain the electronics to read and write data on to the magnetic disk surfaces. It
enables very fast accessibility of data and can store much more amount of data
(40 MB to GB) in capacity.
 Floppy disk: is also called diskette. It is removable and has less capacity compared
to the hard disk. The content of a floppy disk can be erased and re-used a number
of times.
Two characteristics describe floppy disks: Size and Capacity. Size refers to the physical
dimension of the disk and Capacity refers to the amount of information the disk can hold.
B. Optical Storage: It uses the principle of light (laser beam), rather than magnetism to
store information. Optical disks have huge capacity. They are two types of common
optical disk:
1. CD (compact disk)
 CD_R (CD recordable)
 CD_RW (CD rewritable)
 CD_ROM (CD read only memory)
2. DVD (digital versatile disk)
 DVD-ROM
 DVD+R
 DVD+RW
 DVD-RAM

8
 9

Other computer components

 Mother board: is also known as system board (main board) that is the heart of the
computer. It is a large green circuit board that holds: RAM, ROM, CPU and so on.
 Expansion Slots: are also called expansion buses which allow the user to add additional
capabilities like network interface card, TV card, Sound card, internal modem, etc.
 Power Supply: It delivers electrical power to the computer system. The computer
components work with +5V, and + 12V. The power supply steps down the voltage to
the required value and changes AC to DC.
 Ribbon buses (Cables): are used to connect the different components, and transfer
data.
 Ports: A port is the interface through which the microprocessor in the system unit can
communicate with an option such as a monitor or a printer. There are two common
types of ports:
 Serial Ports: Allow data to send and receive serially (a bit at a time) over a
single wire.
 Parallel ports: Data come in parallel over eight parallel wires.
 CMOS Battery (Complementary Metal oxide Semiconductor): It holds (retains) the
configuration or information of the computer.

2. The Computer Software

The hardware alone cannot perform any particular calculation or data manipulation without
being instructed exactly what to do and how to do it. That is, software is a series of instructions
that tell the hardware what to do and how to do it. Software (Program) makes the interface
between the user and the electronic components of the computer. It facilitates communication
between a human being and a machine (the computer). Computer software is divided into two
broad categories:
A. Systems Software
B. Application Software

Application software Systems Software Hardware

User

9
 10

A. Systems Software
Systems software consists of all the programs, languages and documentations supplied by the
manufacturer. These programs allow the user to communicate with the computer and write or
develop its own programs. This software makes the machine easier to use, and makes an
efficient use of the resources of the hardware possible. Systems software provides the interface
between the hardware and the users. Interface is the means by which a person interacts with a
computer. Systems software includes: operating system, system support software, and systems
development software.
 Operating System: is a master control program, permanently stored on the primary
memory that interprets user commands requesting various kinds of services such as
display, print, copy a data file, list all files in a directory, execute a particular program.
 It manages the hardware for the most efficient use of computer resources
 Provide an interface between a user and an application program and the hardware.
Examples of an operating system are: MS-DOS, MS-Windows, and UNIX.
 System Support software:
 It provides system utilities and other operating services.
 It is a border line between application software and system software.
 Operating services consist of programs that provide performance statistics for the
operational staff and security monitors to protect the data and the system.
 System Development Software: includes the computer or programming language
translators that are used to convert written programs to machine language for
execution.
Programming Language
Programming language is the means of communication between a human being and a
computer. The levels of programming language are discussed in terms of generation of
languages. Accordingly, there are four levels of computer programming languages:
I. Machine Language: is the first generation of programming language that was available in
the earliest days of computer.
 It is the only programming language that the computer can understand.

10
 11

 Machine language is the lowest level language which works in the form of 0s & 1s.
II. Assembly Language: Is the second-generation language. Use mnemonics in place of 1s and
0s to represent the operation codes. Mnemonics is an alphabetical abbreviation used as a
memory aid. It uses assembler to translate assembly language to machine language.
III. High-level Languages: Is the third generation language. The instructions are called
statements. Statements closely resemble human languages. The translator of this language
Compilers and Interpreters used as a translator of high-level to machine language. E.g.
FORTRAN, COBOL, BASIC, Pascal, C++, Visual C++, etc.
IV. Fourth Generation Languages: allow users to create programs with much less effort than is
required by high-level languages. They are more English-like than high-level languages.
Examples are database query languages, report generators, and application generators.
B. Applications Software
It consists of programs or instructions to perform specific task or job or information processing
activities. There is a number of application software. Some of such application softwares are:
- Word Processing: Allow creating documents like letters, reports, handouts, office memos,
magazines, newspapers, etc. Examples MS-Word, Word Star, and Word Perfect.
- Spreadsheets: is a table of rows and columns to perform calculations and other related
activities on a numerical data. Examples are MS-Excel, Lotus 1-2-3, and Quattro Pro.
- Database Management system (DBMS): are used to systematically handle, organize, or
store data and latter get the stored data in a much flexible way. Examples: MS-Access
Fox Pro.
- Desktop Publishing Programs: are used to create (publish) professional newsletters and
reports using the PC that sits on your desktop. Examples: Page Maker, Ventura.
- Computer Aided Design (CAD): is used by engineers and designers to draw an object.
Example: Auto CAD
- Computer Games: Example Chess, Solitaire, Dave, etc.

11