Computer systems evolved from basic calculator to a high performance computer system. Since in start we used a single accumulator, but now we are using multiple registers and cache for the same purpose of storing temporary memory. To improve our system performance we also use instruction pipelining.

Pipelining is a term used for a specific type of process in which before the completion of a single instruction we input the next instruction. This is how we use to save our time. The different stages of a pipeline are called assembly line. In an assembly line we input a single instruction and when it goes to the next stage the first slot becomes empty and thus we can send a new instruction to the first stage.

So in simple words we divide a single instruction into a variety of small chunks that are called pipeline stages.

Six basic stages that we must know in order to have an idea about instruction pipelining are as follows

  1. Fetch instruction.
  2. Decode instruction.
  3. Calculate operands.
  4. Fetch operand.
  5. Execute instruction.
  6. Write operand.

All of the above are executed one by one for first cycle, but when the first stage has being executed the next instruction goes into the same pipeline. Thus the propagation or time delay is decreased and we achieve high efficiency.

But there are some problems or we can say disadvantages with pipelining which includes

  1. Data dependency: If the next instruction wants to use the “Updated “data of a previous instruction then there occurs a problem since the pervious instruction is in the pipeline and can’t be modified then.
  2. Interrupts: Interrupts plays an important part in processor but they can cause disorientation in the pipelining.
  3. Brach penalty: By this we mean that a branch can invalidate several instruction fetches.
  4. Memory access: A lot of memory accesses are required for a single instruction like in fetch instruction, fetch operand and write operand.

Thus there are both advantages and disadvantages are present in pipelining but disadvantages can be overcome by different techniques, which I will discuss later.