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The purpose & components of the CPU

Purpose of the CPU

The Central Processing Unit (CPU) is the “brain” of the computer. It:

  • Executes instructions from programs

  • Carries out the fetch-decode-execute cycle

  • Manages the flow of data between the CPU, memory, and input/output devices


Common CPU Components

  • Arithmetic Logic Unit (ALU) performs arithmetic operations (add, subtract) and logical operations (AND, OR, NOT, comparisons).

  • Control Unit (CU) directs the operations of the CPU. It:

    • Decodes instructions.

    • Sends control signals to coordinate components.

    • Oversees the fetch-decode-execute cycle.

  • Cache is small, fast memory inside the CPU that stores frequently accessed data or instructions. Reduces the time needed to access data from main memory.

  • Registers are very fast, small storage locations inside the CPU used to hold data, instructions, or addresses temporarily during processing.


Diagram of a CPU showing labeled components: ALU, CU, and registers (ACC, MAR, MDR, PC), with a cache. Background is dark gradient.

Practise exam question

Practise Questions:

  1. Give the 3 purposes of the CPU in a computer system. 

  2. Explain the purpose of the MAR and MDR in the CPU.


Answers:

  1. Fetch Instructions

  2. Decode Instructions

  3. Execute Instructions

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