Difference Between ALU and CPU

The key difference between ALU and CPU is that the ALU is an electronic circuit which is a subsystem of CPU that performs arithmetic and logical operations while CPU is an electronic circuit that handles instructions to operate the computer.

A computer system consists of both hardware and software. Hardware is the electronic or mechanical components. Software refers to the data and instructions. The essential component to perform the tasks of the computer is the CPU. CPU consist of two main subsystems. They are the ALU and the Control Unit.

CONTENTS

1. Overview and Key Difference
2. What is ALU
3. What is CPU
4. Side by Side Comparison – ALU vs CPU in Tabular Form
5. Summary

What is ALU?

ALU stands for Arithmetic and Logic Unit. It is a subsystem or a component of CPU. The main objective of it is to handles arithmetic and logic operations. Arithmetic operations are addition, subtraction, division, multiplication etc. The logical operations determine whether a statement is true or false. Furthermore, Graphical Processing Units (GPU), Floating Point Units (FPU) also have ALUs. A single CPU, FPU or a GPU can have multiple ALUs to handle advanced calculations.

Figure 01: ALU

ALU performs various calculations. The inputs to it are the data on which it is to operate. They are called operands. In a mathematical expression such as “2+3 = 5”, 2 and 3 are the operands. The ‘+’ is the addition, and it is the operator. The ‘5’ is the result of the performed operation. The status register requires information of the ALU’s previous operations or the current operation. So, there are incoming and outgoing status signals in ALU. An opcode is the machine language instruction that explains what operation it should perform. In brief, that is how the ALU functions.

What is CPU?

CPU (or commonly known as a processor) handles instructions to perform various tasks of the computer. The main subsystems of the CPU are ALU and CU. ALU handles arithmetic and logical operations. The CU that stands for the Control Unit regulates and synchronizes operations of the computer. And it consists of programmable registers and other electronics. Therefore, it fetches instructions from memory, decodes them and directs them to various units to perform the required task.

Memory is an important component for the CPU to function properly. It provides the instructions for the CPU to perform, and also after data processing, the result goes back to the memory for storing. Furthermore, the other components that CPU relies on are system clock, secondary storage, data and address buses. CPU can process 32bit instructions or 64-bit instructions depending on the computer architecture.

Figure 02: CPU

Usually, CPU has a high data transferring capacity. Further, the clock speed indicates the number of instructions it can process within a second. So if the CPU clock speed is 2 GHz, it means that it can process 2 billion instructions each second. In brief, the CPU is the most significant component in the entire computer system.

What is the Difference Between ALU and CPU?

Summary – ALU vs CPU

The difference between ALU and CPU is that ALU is an electronic circuit, which is a subsystem of CPU that performs arithmetic and logical operations while a CPU is an electronic circuit that handles instructions to operate the computer.

Reference:

1.“Central Processing Unit.” Wikipedia, Wikimedia Foundation, 27 Apr. 2018. Available here 
2.“Arithmetic Logic Unit.” Wikipedia, Wikimedia Foundation, 22 Apr. 2018. Available here 

Image Courtesy:

1.’ALU block’By Lambtron – Own work, (CC BY-SA 4.0) via Commons Wikimedia 
2.’Ic-photo-Nintendo–DMG-CPU B–(Gameboy-CPU)’By Myself User:ZyMOS – CPU Grave Yard, my CPU collection, (CC BY-SA 4.0) via Commons Wikimedia

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