Fetch Execute Cycle
The Fetch Execute Cycle is the basic operational process that all computer systems execute in order to process instructions given to them. It is also known as the instruction cycle, instruction cycle fetch-execute cycle, or simply the fetch-execute loop. This cycle occurs for every instruction that is given to the computer, repeating it in an endless loop until the given task is completed or the computer is turned off.
The fetch execute cycle, as the name implies, can be broken into four distinct stages – fetch, decode, execute and store.
In the first stage, the fetch stage, the instruction that the computer needs to process is fetched from memory. This could be from ROM, RAM or a hard disk.
The second stage of the cycle is the decode stage. Here, the instruction taken from memory is decoded so that the computer can understand it. Decoding can involve do a translation from assembly language or machine code into a language comprehensible by the computer.
In the third stage of the cycle, the execute stage, the instruction is carried out based on its instruction code. This will perform a specific operation on items of data and transfer the result to some other memory location.
The final stage is the store stage, where the result of the instruction is stored back in memory for later use.
Once the cycle is complete, the machine searches for the next instruction it needs to fetch and execute from memory and so the entire process repeats itself in an endless loop until the given task is completed or the computer is turned off.
The general format and execution of the fetch-execute cycle remains unchanged from the earliest computers up to the most advanced, though the individual steps involved may be more complex in more advanced machines.
