True and False Questions. Give reasons for your answers. (a) Allowing jumps, bra

Question

True and False Questions. Give reasons for your answers.

(a) Allowing jumps, branches, and ALU instructions to take fewer clock cycles than the five required by the load instruction will increase pipeline performance under all circumstances.

(b) Trying to allow some instructions to take fewer cycles does not help, since the throughput is determined by the clock cycle. (It is true that the number of pipe stages per instruction affects latency, not throughput.)

(c) Allowing jumps, branches, and ALU operations to take fewer cycles only helps when no loads or stores are in the pipeline, so the benefits are small. (d) Since branches and jumps can take fewer cycles, there is some opportunity for improvement in pipelining performance. (You cannot make ALU instructions take fewer cycles because of the write-back of the result.)

(e) We could improve performance if instead of trying to make instructions take fewer cycles, we explore making the pipeline longer, so that instructions take more cycles, but the cycles are shorter.

Explanation / Answer

Answer:-

(a) False

Shortening the ALU operation will not affect the speedup obtained from pipelining. It would not affect the clock cycle, which will be determined by the operation that takes the most time, i.e., instruction fetch or data access.

(b) True.

The pipelining increase the number of simultaneously executing instrutions and the rate at which instructions are started and completed. The pipelining does not reduce the time it takes to complete an individual instruction, also called the latency. The five-stage pipeline still takes 5 clock cycles for the instruclion to complete. So, the pipelining improves instruction throughput rather than the individual instruction.

C) True

The penalty for using the single-cycle design with a fixed clock cycle is significant, but might be considered acceptable for this small instruction set. Historically, ea rly computers with very simple instruction sets did use this implementation technique. However, if we tried to implement the floating-point unit or an instruction set with more complex instructions, this single-cycle design wouldn't work well at all.

D) True

The write-back stage, which places the result back into the register file in the middle of the datapath.

E ) True

The pipelining paradox is that the time from placing a single dirty sock in the washer until it is dried, folded, and put away is not shorter for pipelining; the reason pipelining is faster for many loads is that everything is working in parallel, so more loads are finished pel' hour. Pipelining improves throughput of our laundry system. Hence, pipelining would not decrease the time to complete one load of laundry, but when we have many loads of laundry to do, the improvement in throughput decreases the total time to complete the work.

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