28/03/2016
Basics of Computer
1.1 INTRODUCTION
In this lesson we present an overview of the basic design of a
computer system: how the different parts of a computer system
are organized and various operations performed to perform a
specific task. You would have observed that instructions have to
be fed into the computer in a systematic order to perform a
specific task. Computer components are divided into two major
categories, namely, hardware and software. In this lesson we will
discuss about hardware, i.e., the machine itself and its connected
devices such as monitor, keyboard, mouse etc., as well as
software that makes use of hardware for performing various
functions.
1.2 OBJECTIVES
After going through this lesson you would be able to:
l explain basic organization of computer system
l explain different types of input and output devices
l define Software and its classification
l distinguish between system software and application
software
l describe computer language and its classification
1
2 :: Data Entry Operations
1.3 WHAT IS A COMPUTER?
Computer is a device that transforms data into meaningful
information. Data can be anything like marks obtained by you in
various subjects. It can also be name, age, s*x, weight, height,
etc. of all the students in a class.
Computer can also be defined in terms of functions it can
perform. A computer can i) accept data, ii) store data, iii) process
data as desired, and iv) retrieve the stored data as and when
required and v) print the result in desired format.
The major characteristics of a computer are high speed, accuracy,
diligence, versatility and storage.
1.3.1 Computer Organisation
The block diagram of computer is shown in Fig. 1.1.
Fig. 1.1 Block diagram of Computer Organisation
The computer performs basically five major operations of
functions irrespective of their size and make. These are 1) it
accepts data or instruction by way of input, 2) it stores data, 3) it
can process data as required by the user, 4) it gives results in
the form of output, and 5) it controls all operations inside a
computer. We discuss below each of these operations.
1. Input: this is the process of entering data and programs
into the computer system.
Input unit Output unit
Memory Unit
Control Unit
Arithmetic
Logic Unit
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2. Control Unit (CU): The process of input, output, processing
and storage is performed under the supervision of a unit
called 'Control Unit'. It decides when to start receiving data,
when to stop it, where to store data, etc. It takes care of step
-by-step processing of all operations in side the computer.
3. Memory Unit: Computer is used to store data and
instructions.
4. Arithmetic Logic Unit (ALU): The major operations
performed by the ALU are addition, subtraction,
multiplication, division, logic and comparison.
5. Output: This is the process of producing results from the
data for getting useful information.
The ALU and the CU of a computer system are jointly known as
the central processing unit (CPU). You may call CPU as the brain
of any computer system.
INTEXT QUESTIONS
1. What are the five basic operations performed by the
computer?
2. Define ALU, CU and CPU.
3. Choose the correct answer.
(a) The task of performing arithmetic and logical
operations is called:
(i) ALU (ii) editing (iii) storage (iv) Output
(b) The ALU and CU jointly are known as
(i) RAM (ii) ROM (iii) CPU (iv) None of above
(c) The process of producing results from the data for
getting useful information is called:
(i) output (ii) input (iii) processing (iv) storage
1.4 PERIPHERAL DEVICES
Peripheral devices are connected to the computer externally.
These devices are used for performing some specific functions.
Peripheral devices are as follows:
1. Input Devices
2. Output Devices
3. Other Peripherals
4 :: Data Entry Operations
Fig. 1.2 Different peripheral devices of Computer
1.5 INPUT DEVICES
Input devices accept data and instructions from the user.
Following are the examples of various input devices, which are
connected to the computer for this purpose.
1. Keyboard
2. Mouse
3. Light Pen
4. Optical/magnetic Scanner
5. Touch Screen
6. Microphone for voice as input
7. Track Ball
1.5.1 Keyboard
A keyboard (as shown in figure 1.3) is the most common input
device. Several kinds of keyboards are available, but they
resemble each other with
minor variations. The
keyboard in most common
use is the QWERTY board.
Generally standard
keyboard has 104 keys. In
these keyboards, the cursor
control keys are duplicated
to allow easier use of the
numeric pad.
Monitor
Keyboard
Disk drives
Mouse
Fig. 1.3 Keyboard
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1.5.2 Mouse
A mouse is an electro-mechanical, hand-held device (as shown
in figure 1. 4). It is used as a pointer. It can perform functions
like selecting menu commands, moving icons, resizing windows,
starting programs, and choosing options.
Fig. 1.4 Mouse
The most common mouse uses an internal, magnetically coated
ball, to detect the movement of the mouse across a flat surface,
usually a desktop. Now a days Optical or laser mouse is used to
detect the movement. All windows based applications today are
designed to work with a mouse. A mouse is used to replace hard
-to-remember key combinations with easier "Point and Click"
actions. However, it cannot substitute all keyboard operations.
It can be alternative for commands based operations.
1.5.3 Light pen
An input device that utilizes a light-sensitive
detector to select objects on a display screen.
A light pen is similar to a mouse (as shown in
figure 1.5), except that with a light pen you can
move the pointer and select objects on the
display screen by directly pointing to the
objects with the pen.
1.5.4 Optical Scanner
These devices are used for automatic data collection. The
devices of this category completely eliminate manual input of
data. For example, the bar-code reader is actually just a special
type of image scanner. An image scanner translates printed
Monitor
Disk drives
Mouse
Fig. 1.5 Light Pen
6 :: Data Entry Operations
images into an electronic format that can be
stored in a computer’s memory, and with the
right kind of software, one can alter a stored
image. Another example of scanner is optical
character recognition (OCR) device, used by
banks to convert the scanned image of a
typed or printed page into text that can be
edited on the computer.
1.5.5 Touch Screen
Touch panel displays and pads are now being offered as
alternatives to keyboard. Here the input can be given through the
computer screen, that accepts the input through monitor; users
touch electronic buttons displayed on the screen or they may use
light pen.
Fig. 1.7 Touch Screen Monitor
1.5.6 Microphone
Microphone is an input device, which takes voice as input. The
voice communication is more error-prone than information
through keyboard. There are two types of microphones available
(as shown in figure 1.8):
1. Desktop Microphone
2. Hand held Microphone
Fig. 1.8 Desktop microphone and Hand-held Microphone
Fig. 1.6 Scanner
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1.5.7 Track Ball
Trackball, a pointing device, is a mouse
lying on its back (as shown in figure 1. 9).
To move the pointer, you rotate the ball
with your thumb, your fingers, or the
palm of your hand. There are usually one
to three buttons next to the ball, which
you use just like mouse buttons.
The advantage of trackballs over mouse is that the trackball is
stationary so it does not require much space to use it. In addition,
you can place a trackball on any type of surface, including your
lap. For both these reasons, trackballs are popular pointing
devices for portable computers.
1.6 OUTPUT DEVICES
Output devices return processed data that is information, back
to the user. Some of the commonly used output devices are:
1. Monitor (Visual Display Unit)
2. Printers
3. Plotter
4. Speakers
1.6.1 Monitor
Out of all the output devices,
monitor (as shown in figure
1.10) is perhaps the most
important output device
because people interact with
this device most intensively
than others. Computer
information is displayed,
visually with a video adapter card and monitor. Information
processed within the CPU, that needs to be visually displayed,
is sent to video adapter. The video adapter converts information
from the format used, in the same manner as a television displays
information sent to it by a cable service.
Fig. 1.9 Track Ball
Fig. 1.10 CRT and LCD Monitor
8 :: Data Entry Operations
Two basic types of monitors are used with microcomputers,
which are as follows:
1. CRT
2. LCD
Cathode Ray Tube (CRT): CRT or Cathode Ray Tube Monitor is
the typical monitor that you see on a desktop computer. It looks
a lot like a television screen, and works the same way. This type
uses a large vacuum tube, called cathode ray tube (CRT).
Liquid Crystal Displays (LCD): This type of monitors are also
known as flat panel monitor. Most of these employ liquid crystal
displays (LCDs) to render images. These days LCD monitor are
very popular.
When people talk about the capabilities of various monitors, one
critical statistic is the resolution of the monitor. Most monitors
have a resolution of at least 800 x 600 pixels. High-end monitors
can have resolutions of 1024 x 768 pixels or even 1280 x 1024
pixels. Thus monitors are available either in low resolution or in
high resolution.
1.6.2 Printer
After a document is created on the computer, it can be sent to a
printer for a hard copy (printout). Some printers offer special
features such as colored and large page formats. Some of the
most commonly used printers are:
1. Laser Printer
2. Ink Jet Printer
3. Dot Matrix Printer
4. Line Printer
Laser Printer: A laser printer produces
high quality print that one normally finds
in publishing. It is extremely fast and
quiet. Moreover, the operation of a laser
printer is easy with automatic paper
loading and no smudging or messing up
of ink ribbons. The fastest laser printer Fig. 1.11 Laser Printer
Basics of Computer :: 9
can print up to 200 pages per minute in monochrome (black and
white) and up to 100 pages per minute in colour.
Ink-Jet Printer: An ink-jet printer
creates an image directly on paper by
spraying ink through as many as 64
tiny nozzles. Although the image it
produces is not generally quite as
sharp as the output of a laser printer,
the quality of ink-jet images is still high.
In general, ink-jet printer offers an
excellent middle ground between dot
matrix and laser printer. Like laser printer, an ink-jet printer is
quiet and convenient, but not particularly fast.
Typically, an ink-jet printer is more expensive than a dot-matrix
printer, but costs only half as much as a laser printer.
Dot Matrix Printer: The dot matrix
printer was very popular at one point of
time. It is a very versatile and inexpensive
output device. In dot matrix printer the
print head physically "hits" the paper
through the ribbon and produces text (or
images) by combinations of dots; hence
the name dot matrix printer. Its speed is
measured in characters per second
(CPS). Although it is less expensive, it is
louder, slower and produces lower print
quality.
Line Printer: A line printer is generally
used with large computer systems to
produce text based data processing
reports. Line printers are high-speed
printers with speeds ranging anywhere
from 100 to about 3800 lines per minute.
In the past, print quality on line printers
was not high. Developments in
technology are improving the print quality
on line printers. These are in the cost
range of lacs of Rupees.
Fig. 1.12 Ink-Jet Printer
Fig. 1.13 Dot Matrix
Printer
Fig. 1.14 Line Printer
10 :: Data Entry Operations
1.6.3 Plotter
A plotter is a special kind of output device that, like a printer,
produces images on paper, but does so in a different way. Plotters
are designed to produce large drawings or images, such as
construction plans for buildings or blueprints for mechanical
objects. A plotter can be connected to the port normally used by
a printer.
An array of different colored pens in a clip rack and a robotic arm
is part of plotter. The instructions that a plotter receives from a
computer consist of a color, and beginning and ending
coordinates for a line. With that information, the plotter picks up
the appropriate pen through its arm, positions it at the beginning
coordinates drops the pen down to the surface of the paper and
draws to the ending coordinates. Plotters draw curves by creating
a sequence of very short straight lines.
Plotters usually come in two designs:
1. Flat Bed: Plotters of small size to be kept on table with
restriction of paper size.
2. Drum: These plotters are of big size using rolls of paper of
unlimited length.
Fig. 1.15 Flat bed and Drum Plotter
1.6.4 Speaker
Speakers (as shown in figure 1.16) are
another type of output device, which
allow you to listen to voice like music,
and conversation with people.
Fig. 1.16 Speaker
