NIOS Computer Science Chapter 1 – Anatomy of a Digital Computer Part 3
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Arithmetic Logic Unit (ALU)

It represents the fundamental building block of the central processing unit (CPU) of a computer.

This unit is used to perform all the arithmetic and logic operations, such as addition, multiplication, comparison, etc.
For example: Consider the addition of two numbers A and B. The control unit will select the number A from its location in the memory and load it into the arithmetic logic unit.

Modern CPUs contain very powerful and complex ALUs.

An ALU performs basic arithmetic and logic operations.
Examples of arithmetic operations: addition, subtraction, multiplication, and division.
Examples of logic operations: comparisons of values such as NOT, AND, and OR.
NOT gate
OR gate
AND gate
Control Unit (CU)

The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor.

It tells the computer's memory, arithmetic/logic unit and input and output devices.
CU functions are as follows

Interprets instructions.

Regulates and controls processor timing.

Sends and receives control signals from other computer devices.

Handles multiple tasks, such as fetching, decoding, execution handling and storing results.