Question

Match List - I with List - II. 

List - I		List - II
A.	Pipeline bubble	I.	A deliberate delay or idle slot inserted in pipeline
B.	Pipeline flush	II.	Clearing all in-progress instructions
C.	Data forwarding	III.	Using result before it is written back
D.	Pipeline stall	IV.	Holding stages due to dependency or resource conflict

Choose the correct answer from the options given below:

• A. A-I, B-II, C-III, D-IV
• B. A-II, B-I, C-III, D-IV
• C. A-IV, B-I, C-II, D-III
• D. A-IV, B-III, C-II, D-I

Hint:

Bubble = NOP (Idle). Flush = Reset (Branch taken). Forwarding = Shortcut (Bypass). Stall = Wait (Conflict).

Answer 1

The Correct Option is A

Concept:
• Pipelining improves instruction throughput by overlapping different stages of instruction execution.
• Hazards (Data, Control, or Structural) are situations that prevent the next instruction from executing in the next clock cycle.

Step 1: Match A with I (Pipeline Bubble)
A "bubble" is essentially a NOP (No-Operation) that moves through the pipeline. It is a "deliberate delay or idle slot" used to resolve hazards. So, A matches with I.

Step 2: Match B with II (Pipeline Flush)
When a branch prediction is incorrect, the instructions currently in the earlier stages are wrong. The pipeline must be "flushed" by "clearing all in-progress instructions." So, B matches with II.

Step 3: Match C with III (Data Forwarding)
Data forwarding (or bypassing) is a hardware technique where the result of an operation is routed directly to the next instruction "before it is written back" to the register file. So, C matches with III.

Step 4: Match D with IV (Pipeline Stall)
A stall occurs when the control unit "holds stages" due to a "dependency or resource conflict" that cannot be resolved by forwarding, forcing the instruction to wait. So, D matches with IV.