When an instruction is in the stage C, 4 other instructions can be being prepared (A, B) or in the course of closing (D).
Without Pipeline:
First Instruction Second Instruction.....
With Pipeline:
In a unit with pipeline the circuits are modified in order to be able
to use at the same time all the stages.
When an instruction is in the stage C, 4
other instructions can be being prepared (A, B) or in the course of closing
(D).
Without Pipeline:
First Instruction
Second Instruction.....
With Pipeline:
 |
First Instruction... Second Instruction... Third Instruction... |
Nowadays all PC processors are with pipeline, and Superscalar technologies.
But certain stages need sometimes several cycles to carry out an instruction; sometimes the data used for calculation are not available (access slow report, access discs, makes an attempt interruptions...) and the stage remains stopped during several cycles.
Calculation with pipeline is thus fast but is not been free from the
problems of waiting.
Moreover only one instruction is carried out in the stage of execution:
it is not enough.