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The execution of a computer program requires instruction fetch from memory to CPU and instruction execution. The data transfer and instruction execution need to be completed in a sequence of small steps. Each small step requires a dedicated circuit. Old microprocessors use only a small portion of their circuits at a time instance so many circuits are idle.
Pipelining is an idea that utilizes circuits concurrently so that the computation speed can be increased several times using the same IC fabrication technology. Pipelining uses the “assembly line” concept, that is, executing several instructions at the same time. Each instruction is executed at a different stage of the pipeline. This arrangement does not work well unless the time required at each stage is approximately the same.