Basic Structure of Computers Merin

8/8/2019 Basic Structure of Computers Merin

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Presented by:

Merin Mariam Thomas

Date: 03/09/10

Seminar On

BASIC STRUCTURE OF

COMPUTERS





FUNCTIONAL UNITS

A computer consists of five functionally independent

parts. They are :

* Input unit* Memory unit

* Arithmetic and logic unit

* Output unit

* Control unit.



BASIC FUNCTIONAL UNITS OFA COMPUTER -FIGURE

I/O

INPUT

OUTPUT

MEMORY

Processor

ARITHMETIC

AND LOGIC

CONTROL



OPERATION OFA COMPUTER

Input unit-

accepts coded information from humanoperators from electromechanical devices.

The information received is either :

-stored in computer Memory unit for later reference- or immediately used by ALU to perform desired

operations.

Finally processed information are sent back to outsideworld through Output unit.

Control unit controls all activities inside the machine.



CATEGORIES OF INFORMATION

1. Instructions or machine instructions

Instructions are explicit commands that :

Govern the transfer of information within a computer

as well as between computer and its i/o devices.

Specify the arithmetic and logic operations to beperformed.

2. Data

are numbers and encoded characters that are used asoperands by the instructions.



REPRESENTATION OF INFORMATION

Numbers are encoded in Binary notation called BinaryCodedNotation (BCD).

- Each decimal digit is encoded by 4 bits.

Alphanumeric characters are also encoded in Binarycodes. Schemes used are:

ASCII (American Standard Code for Information

Interchange)

Each character represented as 7 bit code.

EBCDIC (Extended Binary Coded Decimal

Interchange Code)

Each character represented as 8 bit code.



INPUT UNIT

Accepts coded information from electromechanicaldevices over digital communication lines.

Used to read data.

Examples are: Keyboard,mouses,trackballs etc.

OUTPUT UNIT

Counterpart of input unit. Function is to send processed result to the outside

world.

Examples are:Monitors,printers etc.



MEMORY UNIT

Function is to store programs and data.

Classes of storage are:

1.Primary storage.

2. Secondary storage.



PRIMARY STORAGE OR MAIN MEMORY

Fast memory that operates at electronic speeds.

Programs must be stored in memory while they are beingexecuted.

Memory contains large no. of semiconductor storage cells .

Each cell is capable of storing one bit of information.

These cells are processed in groups of fixed size called words.

Contents of one word, containing n bits, can be stored orretrieved in one basic operation.

Given word can be accessed by specifying*its address* issue a control command.



Word length :-The number of bits in each word. It

ranges from 16 to 64 bits.

Data are manipulated within a machine in units of words, multiple words or parts of words.

When the main memory is accessed, usually one wordof data is read from the memory or written to it.

Memory Access Time :-The time required to access one

word.

This time is independent of the location of word beingaccessed.

Ranges from 10 to 100 nanoseconds.

Disadvantage:-Quite expensive.





ARITHMETIC AND LOGIC UNIT (ALU)

Most computer operations are executed in ALU.

All arithmetic and logical operations are carried out inALU.

Example, To add 2 numbers:-

1.The operands are brought to the processor.

2.Addition is performed by ALU.

3. Results are stored in memory or retained inprocessor for immediate use.



Operands are stored in high-speed storage elements

called registers.

Each register can store one word of data.

Access time to registers are very faster.

The control & ALU are many times faster than otherdevices connected to the computer system.

Therefore, a single processor can handle a number of

external devices such as keyboards, displays etc.



CONTROL UNIT

The control unit serves as a coordinator of the memory,arithmetic and logic, and input/output units.

Sends control signals to other units and senses theirstatus.

Timing signals are generated by control unit.

Timing signals are signals that determine when a given

action is to take place.

A large set of control line (wires) carries the signals usedfor timing and synchronization of events in all units.



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Basic Structure of Computers Merin