The Purpose of the CPU (OCR GCSE Computer Science): Revision Notes
📚 Revision Notes
The Purpose of the CPU
The Fetch-Execute Cycle
- The purpose of the CPU is to carry out the processing of data on the computer system
- It performs the fetch-decode-execute cycle.
- The CPU fetches, decodes and executes instructions
Three Stages in the Cycle
1. Fetch
- The address from the PC is copied to the MAR
- Instruction from MAR is fetched and copied to MDR
- The instruction in the MDR is copied to the CIR
- Increment the PC
2. Decode
- The instruction in CIR is decoded by the control unit
- Data may be loaded into the MDR
3. Execute
- The instruction is performed
- The ALU may be used for any logic or calculations
- The result is stored in the accumulator
infoNote
Key Points to Remember
- The CPU is responsible for processing data in a computer system.
- It follows the fetch-decode-execute cycle to process instructions.
- During the fetch stage, the instruction is retrieved and prepared for processing.
- In the decode stage, the control unit decodes the instruction.
- The execute stage involves performing the instruction, often using the ALU for calculations or logic.