GCSE > Computer Science > OCR > GCSE Computer Science > COMPUTER SYSTEMS: Systems architecture > The fetch-execute cycle
Previous Module
Next Module

COMPUTER SYSTEMS: Encoding and compression

COMPUTER SYSTEMS: Network topologies

COMPUTER SYSTEMS: Wired and wireless networks, protocols, and layers

COMPUTER SYSTEMS: Threats to computer systems and networks

COMPUTER SYSTEMS: Operating systems and utility software

ALGORITHMS AND PROGRAMMING: Types of data

ALGORITHMS AND PROGRAMMING: Producing robust programs

ALGORITHMS AND PROGRAMMING: Designing, creating, and refining algorithms

ALGORITHMS AND PROGRAMMING: Artificial Intelligence (AI)

  • The CPU accomplishes its tasks by running something called the fetch-execute cycle, sometimes also called the fetch-decode-execute cycle.
  • The faster the CPU can run this cycle, the faster the computer can run tasks. The average computer can run this cycle billions of times a second!

  • Fetch: 
    • The program counter (PC) holds the address of the next instruction and sends this to memory access register (MAR). 
    • The instruction is retrieved from main memory and placed into the memory data register (MDR), and copied to the current instruction register (CIR).
  • Decode:
    • The control unit (CU) interprets the instruction stored in the CIR.
    • The CU identifies the required operation and the necessary data, registers, or addressing mode.
  • Execute:
    • The indicated operation is carried out: arithmetic/logic operations (via the ALU), data transfer, or control flow. 
    • Results are written back to registers or memory as required.
    • The cycle then repeats for the next instruction.

Unlock The fetch-execute cycle

Subscribe to SnapRevise+ to get immediate access to the rest of this resource.

Premium accounts get immediate access to this resource.

Previous Module
Next Module