The CPU controls the operation (and determines the
configuration) of all other components in the PC, including RAM, buses, and
peripheral devices. Despite its
complex design and construction, however, the CPU cannot perform a single
operation without directions from a program – either permanently stored in
ROM, or temporarily stored in RAM.
|The CPU “executes” a program in memory by continuously
performing a sequence of operations known as the CPU instruction cycle.
The instruction cycle actually consists of four steps, as follows:
- Fetch - get the next instruction from memory.
- Decode - translate the instruction into a form that
the CPU can understand.
- Execute - perform the action as specified in the
- Store - copy the results of the execution back into
memory for future use.