PARROQUIA EL PARAÍSO DE CELÉN

1.0 Introduction 2.0 Objectives 3.0 Main Content

3.1 The Central Processing Unit

3.2 The Arithmetic and Logic Unit (ALU) 3.3 The Control Unit (CU)

3.4 The Small Memory Buffers 4.0 Conclusion

5.0 Summary

6.0 Tutor-Marked Assignment 7.0 References/Further Reading

1.0 INTRODUCTION

The Central Processing Unit comprises of the Arithmetic/Logic Unit (ALU), which is the processing unit; the Control Unit (CU); and the Random Access Memory (RAM). In essence, the CPU also called the Microprocessor, is made up of the Processing Unit (PU), the Internal Memory (IM), and the Control Unit. It should be noted that the CPU and the Storage Units are usually combined as the System Unit and both constitute the "heart" of the personal computer as it accommodates the microprocessor, the memory and disk drives.

2.0 OBJECTIVES

By the end of this unit, you will be able to:

 explain the central processing unit of a computer

 identify the basic components of a computer central processing unit.

3.0 MAIN CONTENT

3.1 The Central Processing Unit (CPU)

As its name denotes, the CPU is the computer's most important component. It does the entire computer's thinking, calculation and runs the programs (series of instructions) that you request. It is also referred

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to as Microprocessor or simply Processor. To perform its function, the CPU chip consists of three main sections:

a) The Arithmetic/Logic Unit (ALU);

b) The Control Unit (CU), and

c) The Small Memory Buffers (or Registers).

Fig. 1.29: Organisation of a Typical Central Processing Unit (CPU)

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Fig. 1.30: Structure of Central Processing Unit (CPU)

Fig. 1.31: Major Parts of a CPU 3.2 The Arithmetic and Logic Unit (ALU)

The ALU contains logical circuitries used to perform arithmetic, logic and manipulation operations on the operand units. These operations can involve single operand or more operands. Special registers necessary for performing arithmetic operations e.g. subtraction, addition, multiplication and division, are located in this unit. These registers are

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used to temporarily hold the operand that is being processed. Electronic circuits called gates are also used by this unit to perform logical operations, e.g. AND, OR, NOT, etc. on operands and to obtain a result in binary form. The ALU also computes values (True or False) represented in binary as 1 or 0, which allow the computer system to make decision during the execution of a program.

3.3 The Control Unit (CU)

The control unit of the CPU generates two types of control signals: 1) the external control signals, and 2) the internal control signals, for the external CPU devices and the internal CPU activities respectively. The CU supervises execution of the instructions of the stored program in the correct sequences. It also activates the appropriate input and output devices, retrieves data from and sends it to the memory, and directs the processor's activities. To perform its functions, the control unit requires a number of special storage locations of its own called register. CU includes the Program Counter (PC) or Sequence Control Register, the Instruction Register (IR), and the Instruction Decoder. Central in the work of the CU is the processor's clock which delivers a steady stream of pulses for timing all transition from event with the CPU. The sequence of operations carried out by the CU may differ from one computer to the other, but the principle is the same.

3.4 The Small Memory Buffers (or Registers)

Both the CU and the ALU require a small amount of temporary storage to hold the instructions and data currently being processed. These small temporary storage units are called registers (or buffers). A register is a small high-speed storage area used to hold important information during CPU operations. In most cases, registers can hold only one number or one instruction. Registers of the CPU are of two types: General-Purpose Registers (GPR) and Special-Purpose Registers (SPR). GPR can be used in a number of different ways. Examples include the Array of Registers, Accumulator, etc. SPR are used to perform specific activities.

Examples are Address buffer, Data buffer, Program Counter (PC), etc.

The registers are the building blocks of the CPU because both CU and ALU also consist of registers.

In-Text Questions

1. Registers are the building blocks of the Central Processing Unit;

True or False?

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2. What are the two types of signals the control unit of the CPU generates?

4.0 CONCLUSION

Haven read this Unit and successfully completed the assessment and self-assessment test, it is assumed that you have attained understanding of the central processing unit of a computer system, and its components.

5.0 SUMMARY

In this Unit, you have learnt about the central processing unit of a computer system. Also, you have learnt about the basic components of a computer CPU. The assessment and self-assessment exercise have been provided to enable you understand your own rating of the learning and understanding you achieved reading this unit.

6.0 TUTOR-MARKED ASSIGNMENT

1. The central processing unit comprises all of the following except 2. Which of the following is not true about the central processing

unit of a computer?

3. What is another name for the CPU of a computer?

4. The CPU and the Storage Units are usually combined as --- 7.0 REFERENCES/FURTHER READING

Bakpo, F. S. (2002). Introduction to Computer Science. Unpublished Material, University of Nigeria Nsukka.

Ikemelu, C. R. (2009). Computer Studies in Secondary Schools:

Implications for Qualitative and Functional Education. Journal of Science Education, 1, 122-129.

McLean, D. D. (2000). Use of Computer-Based Technology in Health, Physical Education, Recreation, and Dance. ERIC Digest.

Ozochinanuife, E. S. (2008). Computer Science for Beginners. His Glory Publications.

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Ozochinanuife, E. S. (2016). New General Computer Course and ICT:

Theory and Practice for Students and others (Revised Edition). His Glory Publications.

Ozochinanuife, E. S. & Ikemelu, C. R. (2019). Computer Science Education: The Journey so far in Nigeria. Journal of Science, Mathematics and Technology Education, 1(1), 284-300.

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UNIT 3 THE OUTPUT UNITS