What is pipelining ? How the idea of pipelining used ina computer ?OR Write a short note on pipelining.

1.Pipelining is a technique of decomposing a sequential process into sub-operations, with each sub-process being executed in a special
dedicated segment that operates concurrently with all other segments.

2. The processor executes a program by fetching and executing instructions, one after the other.

3.Let Fi and E_i refer to the fetch and execute steps for instruction I_i.

4.Execution of a program consists of a sequence of fetch and execute steps as shows is Fig. (A)

Now consider a computer that has two separate hardware units, one for fetching instructions and another for executing them, as shown in Fig. (B).

The instruction fetched by the fetch unit is deposited in an intermediated storage buffer Bi.

The results of execution are deposited in the destination location specified by the instructions.

For these purposes, we assume that both the source and destination of the data operated in by the instructions are inside the block labelled “Execution unit”.

The computer is controlled by a clock whose period is such that the fetch and execute steps of any instruction can be completed in one clock cycle.

Operation of the computer proceeds as in Fig. (C).

In the first clock cycle, the fetch unit fetches an instruction I₁(step F₁) and stores it in buffer B_i at the end of the clock cycle.

In the second clock cycle, the instruction fetch unit proceeds with the fetch operation for instruction I₂ (Step F₂). Meanwhile, the execution unit performs the operation specified by the instruction I₁, which is available to it in buffer B_i(Step E₁). By the end of the second clock cycle, the execution of instruction I₁ is completed and instruction I₂ is available.

Instruction I₂ is stored in B_i by replacing I₁, which is no longer needed. Step E₂ is performed by the execution unit during the third clock cycle, while instruction I₃ is being fetched by the fetch unit. In this manner, both fetch and execute units are kept busy all the time.