Pipeline Hazards: When Operand Data Is Not Available
In a pipelined CPU, instructions overlap across multiple stages (e.g., fetch, decode, execute, memory, write-back). A data hazard arises when an instruction needs an operand value that is not available yet because a preceding instruction that should produce it has not completed the pipeline stages needed to make that value readable. This is why the correct choice in your question is: (i) data hazard.
As one textbook-style description states, a data hazard occurs when the current instruction requires a preceding instruction’s result, but the pipeline does not have enough segments (time) to compute it and write it back in time for the current instruction to read it.
A CPU generally handles these situations using techniques like pipeline stalls (bubbles) and operand forwarding/bypassing.
Key terms for this section: Hazard , Data hazard , Operand forwarding , Pipeline stall.
Footnotes
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Organization of Computer Systems: Pipelining — 5.3.3 Data Hazards - Defines data hazards as insufficient time for producing a value before it’s needed. ↩
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Hazard (computer architecture) - Wikipedia - Describes data hazards and common solutions like forwarding and pipeline stalls. ↩
Why 'operand not available' implies a Data Hazard
- 1Step 1
Pipelining overlaps instructions in time, so a later instruction may reach “operand read” before the earlier instruction has produced the value.
- 2Step 2
If the current instruction depends on the result of a previous instruction (a data dependency), the situation is a candidate hazard.
- 3Step 3
If the required result cannot be read from the register file (or forwarded) when needed, correctness can break.
- 4Step 4
When the problem is specifically that operand data isn’t available in time, the pipeline conflict is a Data hazard.
- 5Step 5
The hardware typically resolves it by inserting a stall/bubble or using forwarding, preventing incorrect computation.
Footnotes
-
Hazard (computer architecture) - Wikipedia - Describes data hazards and common solutions like forwarding and pipeline stalls. ↩
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Pro Tip: Distinguish hazard types
If the issue is timing of operand values, it’s a Data hazard. If the issue is competing for the same hardware resource, it’s a Structural hazard.
Mapping the multiple-choice options
The question asks: “The situation wherein the data of operands are not available is called …”
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(i) data hazard ✅
Because a data hazard is specifically tied to operand/result unavailability in the pipeline when required. -
(ii) stock ❌
Not a standard pipeline hazard term in this context. -
(iii) deadlock ❌
Deadlock is a concurrency/liveness failure (multiple processes wait on each other indefinitely), not a named pipeline hazard category. -
(iv) structural hazard ❌
Structural hazards are resource conflicts where hardware cannot support required simultaneous accesses.
To clarify the distinction:
- Data hazard: operand value not ready
- Structural hazard: same functional unit/memory needed at same time
- Control hazard: branch decision timing
These three common pipeline hazards are described in standard references.
Footnotes
-
Organization of Computer Systems: Pipelining — 5.3.3 Data Hazards - Defines data hazards as insufficient time for producing a value before it’s needed. ↩
-
Pipeline Hazards - GeeksforGeeks (Structural Hazards) - Defines structural hazards as resource conflicts preventing simultaneous access. ↩
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Hazard (computer architecture) - Wikipedia - Notes the three common pipeline hazard types: data, structural, control. ↩
Where the operand becomes available (conceptual)
Where the operand becomes available (conceptual)
title: "Where the operand becomes available (conceptual)timelineItems":
Producer instruction
Stage where result is computed (later)A previous instruction eventually produces the value, e.g., during execute/memory stages."
Consumer instruction
Stage where consumer needs it (earlier)A later instruction reaches operand read, but the value is not ready yet."
Data hazard condition
Hazard detectedIf the pipeline cannot supply the correct operand in time, the CPU must intervene."
Stall or forwarding
ResolutionPipeline stalls (bubbles) and/or forwarding prevent incorrect execution."
Correct vs incorrect option (hazard type match)
“Operand data not available” aligns with data hazards, not structural hazards or others.
Common misconceptions
Knowledge Check
In a pipeline, the situation where the operand data required by an instruction is not available in time is called: