GCSE > Computer Science > AQA > GCSE Computer Science > COMPUTER SYSTEMS: Systems architecture > Purpose and components of the CPU
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  • The Central Processing Unit (CPU) works like the brain of the computer and is responsible for carrying out instructions that make software and hardware work.
  • The CPU’s main responsibilities are to:
    • Carry out instructions from programs
    • Process data inputs from programs and storage
    • Control the rest of the computer system using control signals
Component Function
Arithmetic Logic Unit (ALU)
  • The ALU is responsible for calculations and logic. It performs calculation operations like addition, subtraction, multiplication, and division.
  • It also makes logical comparisons, like checking if one number is greater than the other or if the two values are equal.
  • When the CPU needs to decide between things or carry out a calculation, it uses the ALU.
Control Unit (CU)
  • The CU tells the rest of the computer how to respond to the instructions it receives.
  • It manages the flow of data around the CPU and between the CPU and other components like memory or input/output devices.
  • It sends control signals to other components to coordinate what happens and when, and helps to decode instructions so the CPU knows what action to take.
Cache
  • The cache is a small amount of very fast memory located close to or inside the CPU.
  • It stores frequently used data and instructions, so the CPU doesn’t have to keep going back to RAM, which is much slower. This helps the CPU work faster and more efficiently.
  • There are usually different levels of cache (L1, L2, L3) – the lower the number, the faster and smaller it is.
Registers
  • Registers are tiny memory locations within the CPU itself that store small amounts of data temporarily while instructions are being executed.
  • Registers are the fastest type of memory.
  • Different registers have different roles – for example, some store memory addresses, others store data being worked on.

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