CONTROL UNIT :

It is the center of all the activities of the computer. The control unit contains circuitry that uses electrical signals to direct the entire computer system to carry out or execute stored program instructions.

The control unit does not execute instructions itself, but it tells others what to do.

Arithmetic Logic Unit :

It executes all the arithmetic and logical operations. The arithmetic operations can be Addition, Subtraction, Multiplication, and Division. The logical operations can be: Equal to, Less than and Greater than.

SEMICONDUCTORS

Consisting of very small silicon chips these are mainly used for memory of the computer. They are different types varying in terms of speed and reliability.

lNTEGRATED CIRCUIT

They are nothing but the electronic circuits on a small silicon chip. This chip is capable performing a variety of functions as a substitute for different electronic components of the computer.

HARDWARE

Computer hardware is a collective term used to define the various parts of the computer you can see and touch with your hands. The various components of these are the Monitor, Keyboard and Central Processing Unit.

One can have additional hardware like printer, scanner attached to the computer too.

SOFTWARE

A program is a set of instructions given to the computer to perform a certain task. It is known as the software of the computer. There are two main types of software:

System Softwore

The software used to operate and maintain a computer system and also used by a programmer to develop application software is known as System Software.

Various software under this category are:DOS, Windows, etc. System Software is further classified as (a) Operating system software and (b) language software.

Applicotion Software

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87 The software which performs specific tasks, like railway ticketing, telephone billing, salary and wages calculation, etc., is called the application software.

DATA

It is the raw form of information which is given to the computer for processing.

Data is

name given to the basic facts such as name, age. address, telephone number, etc.

INFORMATION

It is the collection of data in a meaningful form. So all data which has some meaning is

called information. Please remember Data and Information is not the same thing.

Data is raw but information is organized form of data.

PROCESSING

When the data is put into the computer to give some results, the work which the computer performs is called Processing.

BIT

It is the smallest storing space in the computer.

BYTE

A group of 8 bits form a Byte. A computer's capacity is measured in terms of bytes. It is required to store a character—numeric (0 to 9), alphabetic (a to z) or (A to Z) and special characters like these: ! @ # £ % h & * f etc.

But certain large computers can perform operation in parallel, i.e., it can process two or more sets of data simultaneously.

Before an instruction can be executed, program instructions and data must be placed into memory from an input device or a secondary storage device.

CPU Performs the following steps for each instructions:

1. The control unit fetches the instruction from memory (RAM) or cache memory and located to the program register and then to decoder.

2. The control unit decodes the instruction and directs that the necessary data to be moved from memory to ALU.

These first two steps together are called instruction time or I-time 3. The ALU executes the arithmetic or logical instruction.

4. The ALU stores the result of this operation in the appropriate memory position or register

These two steps together are called execution time or E-time. Each ALU unit has an internal clock that produces pulses at a fixed rate to synchronize all computer operations. The repetition of the instruction/execution cycle continues until all the

Srinivas MBA : MIS : CH 4   2009 

88 instructions have been processed. The speed of processing depends on the clock speed of the computer hardware.

The time taken by control unit to process one instruction is called a machine cycle—a Combination of two cycles, i.e., fetch and decode cycle, and execute cycle.

In the fetch and decode cycle phase the control unit obtains an instruction from primary storage(RAM) and stores it in an instruction register and then it decodes the instruction by looking up the instruction's operation code in a table.

Each type of CPU can only understand a particular type of instruction set.

In the execute cycle phase the supervisor control unit executes the instruction by actually performing the task indicated.

Sometimes the instruction simply requires the transfer of data value from one primary Storage location to another, e.g., increment a particular variable. Such type of task does not require the ALU.

MOTHEBOARD

The most important part of the CPU is Motherboard. As the name suggests it is the mother of all boards. All other boards are secondary to it. All instructions pass through this first.

Various components on the motherboard are:

Memory : These slots are there for putting the memory chips. Most of the new motheboards have capacity for 128 MB of RAM.

CPU : This is the main slot for the PC.

Additional : These are there for putting additional attachments like Video card, etc.

BIOS : Basic Input Output Instructions chip which is fixed on the motherboard to run the PC.

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89 Clock This chip is there for providing the running dock within the PC to give you the time and date.

Ports : Most PCs now-a-days come with 2 parallel and 2 serial ports where j can put your mouse, printer, etc.

IDE : These are used for connections to floppy disk, hard disk, CD-ROM drive, etc

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Assignment

1. Write a historical note on evolution of computers ?

2. Write a note on various generations of computers with example ?

3. How computers are classified based on (i) nature of electronic circuits involved ? (ii) by their size ?

4. What are the different blocks of a computer explain the functions of each block ?

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90 CHAPTER 4(b)