Question

Suppose an instruction takes four cycles to execute in a nonpipelined CPU: one cycle to fetch the instruction, one cycle to decode the instruction, one cycle to perform the ALU operation, and one cycle to store the result. In a CPU with a four-stage pipeline, that instruction still takes four cycles to execute, so how can we say the pipeline speeds up the execution of the program?

Answer 1

Answer:

It speeds up the execution because the four-stage pipelined processor can execute the 4 phases simultaneously in different instructions.

Explanation:

Usually, programs have many instructions, and plenty of then do not rely on other operation's result to be executed. Therefore, the pipelined processor can be fetching, decoding, performing operations and storing other instructions that are not in the same dependency chain at the same time.