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Which of the following are NOT true in a pipelined processor?

  1. Bypassing can handle all RAW hazards
  2. Register renaming can eliminate all register carried WAR hazards
  3. Control hazard penalties can be eliminated by dynamic branch prediction
  1. I and II only
  2. I and III only
  3. II and III only 
  4. I, II and III
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(B) I and III

I - False    Bypassing can't handle all RAW hazard, consider when any instruction depends on the result of LOAD instruction, now LOAD updates register value at Memory Access Stage (MA), so data will not be available directly on Execute stage.

II - True, register renaming can eliminate all WAR Hazard.

III- False, It cannot completely eliminate, though it can reduce Control Hazard Penalties
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The correct answer is: II and III only

Explanation:

I. Bypassing can handle all RAW hazards:

  • True. Bypassing (also known as data forwarding) is a technique in pipelined processors to mitigate data hazards. It allows the result of an instruction in a later stage of the pipeline to be directly forwarded to an earlier stage that needs that result. This helps in handling Read-After-Write (RAW) hazards and improving pipeline efficiency.

II. Register renaming can eliminate all register-carried WAR hazards:

  • False. Register renaming helps in eliminating Write-After-Read (WAR) hazards, not Register-Carried Write-After-Read (WAR) hazards. Register renaming is a technique that assigns multiple physical registers to a single architectural register to allow independent execution of instructions, preventing write-after-read hazards. However, it does not eliminate all register-carried WAR hazards.

III. Control hazard penalties can be eliminated by dynamic branch prediction:

  • False. While dynamic branch prediction can significantly reduce the impact of control hazards, it cannot eliminate all control hazards. Dynamic branch prediction techniques aim to predict the outcome of branches and speculatively execute instructions based on those predictions. However, mispredictions can still occur, leading to control hazard penalties.

Therefore, the correct answer is "II and III only."

 

 

 

 

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