1. OCR GCSE (J277) 1.1 The purpose of the CPU - The fetch-execute cycle

Introduction to Computer Systems

• This video is the first in a three-part series on computer systems.

• Focuses on the fetch-execute cycle.

Definition of a Computer

• A computer is an electronic device that:

  • Takes input.

  • Processes data.

  • Delivers output.

• Example of a simple processing task:

  • Input: 5

  • Process: Multiply by 2

  • Output: 10

• Complex example with a game console:

  • Input: Button presses on a controller.

  • Process: Actions carried out by the console.

  • Output: Updates sent to a monitor, sound through a speaker, and possible controller vibrations.

Components of a Computer

• Key components include:

  • Memory (RAM): Stores the program.

  • Central Processing Unit (CPU): Executes instructions.

Fetch-Execute Cycle Overview

• The computer follows a continuous cycle:

  • Fetch: CPU fetches the next instruction from memory.

  • Decode: Inspects and breaks down the instruction.

  • Execute: Carries out the instruction, which may involve:

    • Fetching data from memory.

    • Performing calculations.

    • Storing information back into memory.

• This cycle occurs billions of times per second, referred to as the processor's clock speed.

Clock Speed

• Measured in hertz (Hz).

• 1 Hz = 1 cycle per second.

Recap

• A computer:

  • Takes input, processes data, and delivers output.

• The CPU's role is to:

  • Fetch, decode, and execute instructions from main memory.

• The execution involves various activities based on the instruction.