In a pipelined processor, an instruction needs a result that has not yet been produced by an earlier instruction. If forwarding cannot resolve the dependency, what should the control unit typically do?

Options

  • A. Delete the dependent instruction permanently
  • B. Insert a stall or bubble until the result becomes available
  • C. Disable all registers permanently
  • D. More than one of the above
  • E. None of the above

Correct Answer (Detailed Explanation is Below)

B. Insert a stall or bubble until the result becomes available

Detailed Explanation

Correct Answer: Insert a stall or bubble until the result becomes available.

Explanation: This is a data hazard. If forwarding cannot provide the required operand in time, hazard-detection logic can cause the pipeline to stall by delaying the dependent instruction and inserting a bubble. Once the data becomes available, execution can continue. The exact mechanism depends on the processor architecture.
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BPSC TRE 4 operating system practice set 3

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