LESSON 2
COMPUTER ORGANISATION
2.1 INTRODUCTION
In the
previous lesson we discussed about the evolution of computer. In this lesson we will provide you with an
overview of the basic design of a computer. You will know how different parts
of a computer are organised and how various operations are performed between
different parts to do a specific task. As you know from the previous lesson the
internal architecture of computer may differ from system to system, but the
basic organisation remains the same for all computer systems.
2.2 OBJECTIVES
At the end of the lesson you will be able to:
· understand basic organisation of computer system
· understand the meaning of Arithmetic Logical Unit,
Control Unit and Central Processing Unit
· differentiate between bit , byte and a word
· define computer memory
· differentiate between primary memory and secondary
memory
· differentiate between primary storage and secondary
storage units
· differentiate between input devices and output devices
2.3 BASIC
COMPUTER OPERATIONS
A computer
as shown in Fig. 2.1 performs basically five major operations or functions
irrespective of their size and make. These are 1) it accepts data or
instructions 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 in to the computer system. You should know that computer is
an electronic machine like any other machine which takes as inputs raw data and
performs some processing giving out processed data. Therefore, the input unit
takes data from us to the computer in an organized manner for processing.
2. Storage: The process of saving data and
instructions permanently is known as storage. Data has to be fed into the
system before the actual processing starts. It is because the processing speed
of Central Processing Unit (CPU) is so fast that the data has to be provided
to CPU with the same speed. Therefore the data is first stored in the storage
unit for faster access and processing. This storage unit or the primary storage
of the computer system is designed to do the above functionality. It provides
space for storing data and instructions.
The storage
unit performs the following major functions:
· All data and instructions are stored here before and
after processing.
· Intermediate results of processing are also stored
here.
3. 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.
4. Output: This is the process of producing
results from the data for getting useful information. Similarly the output
produced by the computer after processing must also be kept somewhere inside
the computer before being given to you in human readable form. Again the output
is also stored inside the computer for further processing.
5.Control: The manner how instructions are
executed and the above operations are performed. 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 in side the computer.
2.4 FUNCTIONAL
UNITS
In order to
carry out the operations mentioned in the previous section the computer
allocates the task between its various functional units. The computer system is
divided into three separate units for its operation. They are 1) arithmetic
logical unit, 2) control unit, and 3) central processing unit.
2.4.1 Arithmetic
Logical Unit (ALU)
After you
enter data through the input device it is stored in the primary storage unit.
The actual processing of the data and instruction are performed by Arithmetic
Logical Unit. The major operations performed by the ALU are addition,
subtraction, multiplication, division, logic and comparison. Data is
transferred to ALU from storage unit when required. After processing the output
is returned back to storage unit for further processing or getting stored.
2.4.2 Control
Unit (CU)
The next
component of computer is the Control Unit, which acts like the supervisor
seeing that things are done in proper fashion. The control unit determines the
sequence in which computer programs and instructions are executed. Things like
processing of programs stored in the main memory, interpretation of the
instructions and issuing of signals for other units of the computer to execute
them. It also acts as a switch board operator when several users access the
computer simultaneously. Thereby it coordinates the activities of computer’s
peripheral equipment as they perform the input and output. Therefore it is the
manager of all operations mentioned in the previous section..
2.4.3 Central
Processing Unit (CPU)
The ALU and
the CU of a computer system are jointly known as the central processing unit.
You may call CPU as the brain of any computer system. It is just like brain
that takes all major decisions, makes all sorts of calculations and directs
different parts of the computer functions by activating and controlling the
operations.
Personal Computer Configuration
Now let us
identify the physical components that make the computer work. These are
1. Central
Processing Unit (CPU)
2. Computer
Memory (RAM and ROM)
3. Data bus
4. Ports
5.
Motherboard
6. Hard disk
7. Output Devices
8. Input
Devices
All these
components are inter-connected for the personal computer to work.
IN-TEXT QUESTIONS 1
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 known as
(i) RAM (ii) ROM (iii) CPU
(iv) none of the above
(c) The process of producing results
from the data for getting useful information
(i) output (ii)input (iii) processing (iv) storage
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