The Fetch Decode Execute Cycle

Software instructions processed by the CPU are always in machine language. 

This is all the CPU, or more precisely the control unit, can understand. The method of executing each machine language statement is hardwired within the CPU. 

Each machine language instruction corresponds to a precise series of CPU operations. These CPU operations are known as microcode.

The fetch-execute cycle is used to carry out each and every machine language instruction. This cycle can be split into instruction time (I-time) and execution time (E-time). 

  • Instruction time involves fetching the instruction from memory and then decoding it. 
  • Execution time involves executing the instruction and storing the result. The fetch-execute cycle occurs at a constant pace. 
  • The system clock determines this pace. 
  • At each tick of the clock a part of the fetch-execute cycle occurs.

If you want to see how the Fetch Execute Cycle works in more detail, then the following video will explain the role of the assembly language as well as the main components of the CPU used in the cycle.  It is in a little more depth than you need but it is still interesting and informative.

Fetch execute walk-through using a simplified processor model




Comments