- Concept of fetch-execute cycle. 11 ATAR, 12 GEN
- Purpose and stages (fetch, decode, execute, store) of fetch-execute cycle. 12 ATAR
What is the fetch-execute cycle and why do we need it?
- Also known as the instruction cycle, the fetch-execute cycle is the basic operation cycle of a computer
- It's the process in which a computer receives information (data) and determines what to do with said data
- This cycle is run continuously by the central processing unit (CPU)
- The process follows four phases: fetch, decode, execute and store
- Read The Computing Teacher's article on the Central Processing Unit here
Which parts in the CPU complete the fetch-execute cycle?
- Three main parts inside the CPU that do this are; the registers, the control unit and the Arithmetic Logic Unit (ALU)
- The CPU collects an instruction and prepares it for decoding
- The instruction is collected from a memory location.
- The decoder in the control unit works out (decodes) what to do with the instruction
- Each CPU is designed to understand a specific set of commands
- These commands are referred to as the instruction set
- These instruction sets work by providing the CPU with machine code (hexadecimal or binary instructions)
- The Arithmetic Logic Unit (ALU) then executes the decoded instructions
- These instructions can be arithmetic (manipulation of numbers) or logical processes
- The data from the fetch phase of the cycle is manipulated according to the instructions received from the program
- All the steps above can be seen as prerequisites for the execute phase
- Send and write the results back in main memory.
- The newly processed data is then passed back in to memory fresh from its processing via the data bus. The data can be re-submitted for further processing or be used for a practical use, such as reporting and other outputs. (See: The Computing Teacher's article on the Flow of Data).
More explanation (see attached)
- Wikipedia has a very good article here.
- The Fetch Execute Cycle learning and test at BBC Bitesize
- The CPU and the Fetch Execute Cycle by BBC here
Worksheet and Practice (yet to be added)
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