Introduction to Computing. .

In this chapter will try to understand the basic organization of a processor.

Central Processing Unit

A central processing Unit consists of two parts.

1. Control Unit

2. ALU .

Register

1. In a computer, a register is one of a small set of data holding places that are part of a computer processor . A register may hold a computer instruction , a storage address, or any kind of data (such as a bit sequence or individual characters)

Control Unit

2. Control Unit , does not do any processing

3. It instructs computer what instruction to carry, and how to carry them.

4. It is more like a nervous system of a computer .

5. It manages and coordinates, the entire computer system including its input and out put.

6. Control Unit with help of registers and decoders fetch information and help the system to execute them,.

7. The Control unit consists of Decoder, Program control register ,instruction set, memory address register , Input out put register , general purpose register .

a. Decoder

Decoder decode the instructions and interrupt their meanings

b. Special Purpose Register

i. Instruction registers

Instruction register hold the current instruction , which is passed to decoder

ii. Control Register

It contains the next instruction that is to be executed

Arithmetic Logic Unit

1. An arithmetic-logic unit (ALU) is the part of a computer processor (CPU) that carries out arithmetic and logic operations

2. Execution takes place in ALU .

3. It performs two type of functions using special registers and circuitry . Arithmetic and Logical

a. Mathematical operation

Addition Subtraction etc

b. Logical Operations

Greater than , small than equal to .

Instruction Sets

1. Every Computer has some codes (instructions) which helps us to understand which operation is r be carried out. The set of these instructions i s called Instruction set.

2. 2. Different computer can have different number of instructions tes .

3. Each system has unique instruction set. A program written for a computer having one instruction se (on machine level) will not run on any other computer .

4. CPUs having similar sets , are grouped in to family.

5. “Back ward capability “ is important factor , while designing new instruction sets .

Few of the common and most widely used registers are.

Memory Address Register

It holds the address of active memory location . It stores the address of the memory , where data is being read

Program Control Register

We, know that for running a purpose tasks , instructions needs to be carried out in a particular way. Program, register , holds the address of the next instruction to be executed,

Instruction Register

As program Control register hold the address of the next instruction to be executes, Instruction register hold the address og the current address that is being executed.

Memory Buffer Register

A register utilized to temporarily store information that awaits to be written to, or read from, memory

Accumulator Register

An accumulator is a register in which intermediate arithmetic and logic results are stored. Normally a computer store more than one arithmetic Register .,

Input / Out put Register

The system use this register to communicate with devices, For example, input devices ,sends it data to input register .

xs

Name of Register		Function
MAR		Accumulates results and data
MBR		Hold instruction address while being executed
Program Control		Hold the address of active memory
A		Communicate with I/O devices
I		Hold the address of next instruction to be executed
I/O		Hold the information on its way to memory and from memory

Questions

1. What are two main components of CPU. Explain them.

2. What is microprocessor.

3. What is difference between microcontroller and microprocessor .

4. How a computer is associated with family

5. Why back ward compatibly is important

6. What is the role of decoder ,

7. Why programs written in machine language for one system does not run on other

8. What are register. Name few of them and explain them .

9. What does register length means .