fetch-execute cycle definition architecture, processor
The sequence of actions that a central processing unit
performs to execute each machine code
instruction in a program.
At the beginning of each cycle the CPU presents the value of the program counter
on the address bus
. The CPU then fetches the instruction from main memory
(possibly via a cache
and/or a pipeline
) via the data bus
into the instruction register.
From the instruction register, the data forming the instruction is decoded and passed to the control unit
which sends a sequence of control signals to the relevant function units of the CPU to perform the actions required by the instruction such as reading values from registers
, passing them to the ALU
to add them together and writing the result back to a register.
The program counter is then incremented to address the next instruction and the cycle is repeated.
The fetch-execute cycle was first proposed by John von Neumann