CPU Components & Their Function (AQA GCSE Computer Science): Revision Note

CPU Components & Their Function

What is the Von Neumann architecture?

• The Von Neumann Architecture is a design of the CPU which was proposed by Mathematician John Von Neumann in the 1940s, which most general-purpose computers are built upon

• The Von Neumann Architecture outlines how the computer memory, input / output devices and processor all work together 

What are the components of the CPU?

• The CPU is made up of 5 key components

  • Arithmetic Logic Unit (ALU)

  • Control Unit (CU)

  • Clock

  • Registers

  • Bus

• Each of the components sits within the CPU

What is the function of each component?

Arithmetic logic unit (ALU)

• Performs arithmetic operations

• Performs logical decisions

  • IF X > 5 THEN
          DO ……….

Control unit (CU)

• Coordinates how data moves around the CPU by sending a signal to control the movement of the data 

• Decodes the instructions fetched from memory

Clock

• Keeps related components in sync by generating pulses at a constant rate

Registers

• Extremely small, extremely fast memory located in the CPU

• Hold small amounts of data needed as part of the fetch-execute cycle

• Each register has its own specific purpose

  • Accumulator (ACC) - stores results of logical or arithmetic calculations carried out by the ALU

  • Memory address register (MAR) - stores the address of the next instruction to be fetched from RAM

  • Memory data register (MDR) - stores the data retrieved from RAM

  • Program counter (PC) - stores the memory address of the next instructions to be executed & Increments by 1 as the fetch-decode-execute cycle runs

Bus

• A bus is a collection of wires through which data/signals are transmitted from one component to another