SS 2 WEEK EIGHT LESSON NOTE

 

Ss 2

TOPIC: The central Processing Unit

Introduction

CPU is an acronym for central processing unit, which is considered to be the brain of a computer. The central processing units of personal computers are generally implemented on a single chip called a microprocessor.

How the CPU works

The CPU is centrally located on the motherboard. Since the CPU carries out the large share of the work in the computer, data pass continually through it. The data comes from the RAM and the units (keyboard, drives, etc.). after processing, the data is sent back to the RAM and the units. The CPU continually receives instructions to be executed. Each instruction is a data processing order. The work itself consists mostly of calculations and data transport.

The Instruction-Execution Cycle

Many types of personal computers can execute instructions in less than one-millionth of a second; supercomputers can execute instructions in less than one-billionth of a second.

The CPU performs four steps in executing an instruction:

1.     The control units gets the instruction from the memory

2.     The control unit decides what the instruction means and directs the necessary data to be moved from the memory to the arithmetic logic unit.

3.     The arithmetic logic unit performs the actual operation on the data.

4.     The result of the operation is stored in the memory or a register.

The first two instruction make what is called the instruction time. The last two instructions make up what is called the execution time.

The combination of these two is called a machine cycle. Each central processing unit has an internal clock (or system clock), which produces pulses at a fixed rate to synchronize all computer operations. a single machine cycle instruction is made up of a number of sub-instructions, each of which must take at least one clock cycle.

Components of Central Control Unit

The components of the central processing units are:

I.            Arithmetic logic unit

II.            Memory or storage unit

III.            Control unit

Arithmetic logic unit: this unit consists of two sub-section namely: Arithmetic section and logic section. The function of the arithmetic section is to perform arithmetic operations like addition, subtraction, multiplication and division. The function of the logic section is to perform logic operations such as comparing, selecting, matching and merging data.

Memory unit: This unit can store instruction, data and intermediate results. This unit supplies information to the other units of the computer when needed.

Control unit: the control unit coordinates the components of the computer system. It fetches the code of all the instructions in the program. It directs the operation of the other units by providing timing and control signals. 





 

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