In a pipelined processor, what are the main types of hazards that can occur, and how are they typically avoided?

Introduction / Context:
Pipelining is a key technique used in modern processors to increase instruction throughput by overlapping different stages of execution. However, pipelining introduces hazards that can prevent the next instruction from executing in the next cycle. Understanding the types of hazards and the strategies used to handle them is fundamental in computer architecture.

Given Data / Assumptions:

• We assume a basic pipelined processor with stages such as fetch, decode, execute, memory, and write back.
• The question asks for the different types of hazards in such a system.
• We also consider common methods used to avoid or reduce the impact of these hazards.

Concept / Approach:
There are three primary categories of pipeline hazards. Structural hazards occur when hardware resources are insufficient to support all concurrent operations. Data hazards arise when instructions depend on the results of previous instructions that have not yet completed within the pipeline. Control hazards (or branch hazards) occur due to changes in the flow of control, primarily from branch instructions. Designers use techniques such as pipeline stalls, operand forwarding, out of order execution, branch prediction, and speculative execution to reduce the performance penalties caused by these hazards.

Step-by-Step Solution:
Step 1: Recall the three categories of pipeline hazards: structural, data, and control hazards.Step 2: For structural hazards, remember that they arise when two stages need the same hardware resource in the same cycle, such as a single memory unit for both instruction fetch and data access.Step 3: For data hazards, think about instructions that read a register soon after another instruction writes to it. Without special handling, the later instruction may see the old value.Step 4: For control hazards, consider what happens when a branch changes the instruction flow and the pipeline has already fetched incorrect instructions.Step 5: Match these ideas to the option that correctly lists structural, data, and control hazards and mentions realistic avoidance strategies.

Verification / Alternative check:
Standard computer architecture textbooks describe exactly these three hazard types and present hardware and software techniques to mitigate them. For example, operand forwarding and hazard detection units help with data hazards, while branch prediction reduces control hazards. Additional functional units or separate instruction and data memories can reduce structural hazards. The presence of all three in the same option confirms that it is the correct choice.

Why Other Options Are Wrong:
Option B: Uses terms from programming language theory and runtime errors, not the hardware hazards of pipeline execution.Option C: Incorrectly claims that only structural hazards exist and denies the well known data and control hazards.Option D: Talks about electrical hazards such as electric shock, which are safety issues, not pipeline hazards.

Common Pitfalls:
Students sometimes confuse data hazards with logical programming bugs, but data hazards occur even when the program is correct because of overlapping execution stages. Another mistake is to think that a good compiler can completely eliminate hazards. While compilers can reorder and schedule instructions to reduce hazards, hardware mechanisms are still needed. Understanding the classification helps when analyzing pipeline timing diagrams and performance.

Final Answer:
The correct answer is Structural, data, and control hazards that are handled using techniques like forwarding, stalling, and branch prediction.