BASIC CONCEPTS OF COMPUTER
1.1 INTRODUCTION
A computer is a programmable machine designed to perform
arithmetic and logical operations automatically and sequentially on the input
given by the user and gives the desired output after processing. Computer
components are divided into two major categories namely hardware and software.
Hardware is the machine itself and its connected devices such as monitor,
keyboard, mouse etc. Software are the set of programs that make use of hardware
for performing various functions.
1.2 OBJECTIVES
After going through this lesson you would be able to:
familiarise yourself with characteristics of computers identify the basic
components of a computer explain the importance of various units of a
computer differentiate between system software and application software
explain the importance of operating system get acquainted with open source
appreciate the need of computer security
1.3 CHARACTERISTICS OF COMPUTERS
The characteristics of computers that have made them so
powerful and universally useful are speed, accuracy, diligence, versatility and
storage capacity. Let us discuss them briefly.
Speed
Computers work at an incredible speed. A powerful computer
is capable of performing about 3-4 million simple instructions per second.
Accuracy
In addition to being fast, computers are also accurate.
Errors that may occur can almost always be attributed to human error
(inaccurate data, poorly designed system or faulty instructions/programs
written by the programmer)
Diligence
Unlike human beings, computers are highly consistent. They
do not suffer from human traits of boredom and tiredness resulting in lack of
concentration. Computers, therefore, are better than human beings in performing
voluminous and repetitive jobs.
Versatility
Computers are versatile machines and are capable of
performing any task as long as it can be broken down into a series of logical
steps. The presence of computers can be seen in almost every sphere –
Railway/Air reservation, Banks, Hotels, Weather forecasting and many more.
Storage Capacity
Today’s computers can store large volumes of data. A piece
of information once recorded (or stored) in the computer, can never be
forgotten and can be retrieved almost instantaneously.
1.4 COMPUTER ORGANIZATION
Basic Concepts of Computer
A computer system (fig.1.1) consists of mainly four basic
units; namely input unit, storage unit, central processing unit and output
unit. Central Processing unit further includes Arithmetic logic unit and control
unit, as shown in Figure 1.2.
A computer performs five major operations or functions
irrespective of its size and make. These are it accepts data or instructions
as input, it stores data and instruction it processes data as per the
instructions, it controls all operations inside a computer, and it gives
results in the form of output.
1.4.1 Functional Units:
a. Input Unit: This unit is used for entering data and
programs into the computer system by the
user for processing.
Fig. 1.2: Basic computer Organization
b. Storage Unit: The storage unit is used for storing data
and instructions before and after processing.
– – – –
Dotted lines (– – – –) indicate flow of instruction solid
lines (–––––) indicate flow of data
4 :: Computer and Office Applications
c. Output Unit: The output unit is used for storing the
result as output produced by the computer after processing.
d. Processing: The task of performing operations like
arithmetic and logical operations is called processing. The Central Processing
Unit (CPU) takes data and instructions from the storage unit and makes all
sorts of calculations based on the instructions given and the type of data
provided. It is then sent back to the storage unit. CPU includes Arithmetic
logic unit (ALU) and control unit (CU)
Arithmetic Logic Unit: All calculations and comparisons,
based on the instructions provided, are carried out within the ALU. It performs
arithmetic functions like addition, subtraction, multiplication, division and
also logical operations like greater than, less than and equal to etc.
Control Unit: Controlling of all operations like input,
processing and output are performed by control unit. It takes care of step by
step processing of all operations inside the computer.
1.4.2 Memory
Computer’s memory can be classified into two types; primary
memory and secondary memory
a. Primary Memory can be further classified as RAM and ROM.
RAM or Random Access Memory is the unit in a computer
system. It is the place in a computer where the operating system, application
programs and the data in current use are kept temporarily so that they can be
accessed by the computer’s processor. It is said to be ‘volatile’ since its
contents are accessible only as long as the computer is on. The contents of RAM
are no more available once the computer is turned off.
ROM or Read Only Memory is a special type of memory which
can only be read and contents of which are not lost even when the computer is
switched off. It typically contains manufacturer’s instructions. Among other
things, ROM also stores an initial program called the ‘bootstrap loader’ whose
function is to start the operation of computer system once the power is turned
on.
b. Secondary Memory
RAM is volatile memory having a limited storage capacity.
Secondary/auxiliary memory is storage other than the RAM. These include devices
that are peripheral and are connected and controlled by the computer to enable
permanent storage of programs and data.
Secondary storage devices are of two types; magnetic and
optical. Magnetic devices include hard disks and optical storage devices are
CDs, DVDs, Pen drive, Zip drive etc. Hard Disk
Fig. 1.3: Hard Disk
Hard disks are made up of rigid material and are usually a
stack of metal disks sealed in a box. The hard disk and the hard disk drive
exist together as a unit and is a permanent part of the computer where data and
programs are saved. These disks have storage capacities ranging from 1GB to 80
GB and more. Hard disks are rewritable.
Compact Disk
Compact Disk (CD) is portable disk having data storage
capacity between 650-700 MB. It can hold large amount of information such as
music, full-motion videos, and text etc. CDs can be either read only or read
write type. Digital Video Disk
Digital Video Disk (DVD) is similar to a CD but has larger
storage capacity and enormous clarity. Depending upon the disk type it can
store several Gigabytes of data. DVDs are primarily used to store music or
movies and can be played back on your television or the computer too. These are
not rewritable.
1.4.3 Input / Output Devices:
These devices are used to enter information and instructions
into a computer for storage or processing and to deliver the processed data to
a user. Input/Output devices are required for users to communicate with the
computer. In simple terms, input devices bring information INTO the computer
and output devices bring information OUT of a computer system. These
input/output devices are also known as peripherals since they surround the CPU
and memory of a computer system.
a) Input Devices
An input device is any device that provides input to a
computer. There are many input devices, but the two most common ones are a
keyboard and mouse. Every key you press on the keyboard and every movement or
click you make with the mouse sends a specific input signal to the computer.
Keyboard: The keyboard is very much like a standard typewriter keyboard with a
few additional keys. The basic QWERTY layout of characters is maintained to
make it easy to use the system. The additional keys are included to perform
certain special functions. These are known as function keys that vary in number
from keyboard to keyboard. (see fig.
1.4)
Fig. 1.4: Keyboard
Mouse: A device that controls the movement of the cursor
or pointer on a display screen. A mouse is a small object you can roll along a
hard and flat surface (Fig. 1.5). Its name is derived from its shape, which
looks a bit like a mouse. As you move the mouse, the pointer on the display
screen moves in the same direction.
Fig. 1.5: Mouse
Trackball: A trackball is an input device used to enter
motion data into computers or other electronic devices. It serves the same
purpose as a mouse, but is designed with a moveable ball on the top, which can
be rolled in any direction. Touchpad: A touch pad is a device for pointing
(controlling input positioning) on a computer display screen. It is an
alternative to the mouse. Originally incorporated in laptop computers, touch
pads are also being made for use with desktop computers. A touch pad works by
sensing the user’s finger movement and downward pressure. Touch Screen: It
allows the user to operate/make selections by simply touching the display
screen. A display
Function Keys
Numeric Keypad
Cursor Movement Keys
Alphanumeric Keypad/
Special-function Keys
screen that is sensitive to the touch of a finger or stylus.
Widely used on ATM machines, retail point-of-sale terminals, car navigation
systems, medical monitors and industrial control panels. Light Pen: Light pen
is an input device that utilizes a light-sensitive detector to select objects
on a display screen. (Fig. 1.6)
Fig. 1.6 Light Pen
Magnetic ink character recognition (MICR): MICR can
identify character printed with a special ink that contains particles of magnetic
material. This device particularly finds applications in banking industry.
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 in tests such as aptitude
test. Bar code reader: Bar-code
readers are photoelectric scanners that read the bar codes or vertical zebra
strips marks, printed on product containers. These devices are generally used
in super markets, bookshops etc. Scanner: Scanner is an input device that can
read text or illustration printed on paper and translates the information into
a form that the computer can use. A scanner works by digitizing an image. (Fig. 1.7)
Fig. 1.7 Scanner
b. Output Devices:
Output device receives information from the CPU and presents
it to the user in the desired from. The processed data, stored in the memory of
the computer is sent to the output unit, which then converts it into a form
that can be understood by the user. The output is usually produced in one of
the two ways – on the display device, or on paper (hard copy). Monitor: is
often used synonymously with “computer screen” or “display.” Monitor is an
output device that resembles the television screen (fig. 1.8). It may use a
Cathode Ray Tube (CRT) to display information. The monitor is associated with a
keyboard for manual input of characters and displays the information as it is
keyed in. It also displays the program or application output. Like the
television, monitors are also available in different sizes.
Fig. 1.8: Monitor
Printer: Printers are used to produce paper (commonly
known as hardcopy) output. Based on the technology used, they can be classified
as Impact or Non-impact printers.
Impact printers use the typewriting printing mechanism
wherein a hammer strikes the paper through a ribbon in order to produce output.
Dot-matrix and Character printers fall under this category.
Non-impact printers do not touch the paper while printing.
They use chemical, heat or electrical signals to etch the symbols on paper.
Inkjet, Deskjet, Laser, Thermal printers fall under this category of printers.
Plotter: Plotters are used to print graphical output on paper. It interprets
computer commands and makes line drawings on paper using multicoloured
automated pens. It is capable of producing graphs, drawings, charts, maps etc.
(Fig. 1.9)
Fig. 1.9 Plotter
Facsimile (FAX): Facsimile machine, a device that can send
or receive pictures and text over a telephone line. Fax machines work by
digitizing an image.
Sound cards and Speaker(s): An expansion board that
enables a computer to manipulate and output sounds. Sound cards are necessary
for nearly all CD-ROMs and have become commonplace on modern personal
computers. Sound cards enable the computer to output sound through speakers
connected to the board, to record sound input from a microphone connected to
the computer, and manipulate sound stored on a disk.
1.5 COMPUTER SOFTWARE
Computer software is the set of programs that makes the
hardware perform a set of tasks in particular order. Hardware and software are
complimentary to each other. Both have to work together to produce meaningful
results. Computer software is classified into two broad categories; system
software and application software.
1.5.1 System Software:
System software consists of a group of programs that control
the operations of a computer equipment including functions like managing
memory, managing peripherals, loading, storing, and is an interface between the
application programs and the computer. MS DOS (Microsoft’s Disk Operating
System), UNIX are examples of system software.
1.5.2 Application software:
Software that can perform a specific task for the user, such
as word processing, accounting, budgeting or payroll, fall under the category
of application software. Word processors, spreadsheets, database management
systems are all examples of general purpose application software.
Types of application software are: Word processing
software: The main purpose of this software is to produce documents. MS-Word,
Word Pad, Notepad and some other text editors are some of the examples of word
processing software. Database software: Database is a collection of related
data. The purpose of this software is to organize and manage data. The
advantage of this software is that you can change the way data is stored and
displayed. MS access, dBase, FoxPro, Paradox, and Oracle are some of the
examples of database software. Spread sheet software: The spread sheet
software is used to maintain budget, financial statements, grade sheets, and
sales records. The purpose of this software is organizing numbers. It also
allows the users to perform.
simple or complex calculations on the numbers entered in
rows and columns. MS-Excel is one of the example of spreadsheet software.
Presentation software: This software is used to display the information in the
form of slide show. The three main functions of presentation software is
editing that allows insertion and formatting of text, including graphics in the
text and executing the slide shows. The best example for this type of
application software is Microsoft PowerPoint. Multimedia software: Media players
and real players are the examples of multimedia software. This software will
allow the user to create audio and videos. The different forms of multimedia
software are audio converters,
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