Question

(a) List and explain three types of pipeline hazards.

(b) List and explain three types of cache misses.

(c) What is the principle of locality?

(d). Discuss the advantage and disadvantage of the write back and write through policy in the cache.

Answer 1

a). Three Types Of Pipeline Hazards

• Structural Hazards: They arise from conflicts when the hardware cannot support all possible combinations of instructions in simultaneous overlapped execution.
• Data Hazards: They arise when an instruction depends on the result of previous instruction in way that is exposed by overlapping of instructions in the pipeline.
• Control Hazards: They arise from pipelining of branches and other instructions that change PC.

b).Three Types Of Cache Misses

• Compulsory Miss: It is also known as cold start misses or first references misses. These misses occur when first access to a block happens. Block must be brought into cache.
• Capacity Miss: These misses occur when the program working set is much larger than the cache capacity. Since Cache can not contain all blocks needed for program execution, so cache discards these blocks.
• Conflict Miss: It is also known as collision misses or interference misses. These misses occur when several blocks are mapped to same set or block frame.These misses occur in set associative or direct mapped block placement strategies.

c).Principle Of Locality

• It refers to phenomenon in which computer program tends to access same set of memory locations for particular time period. In other words, Locality of Reference refers to tendency of computer program to access instructions whose addresses are near one another. The property of locality of reference is mainly shown by loops and subroutine calls in a program.

d).Advantage And Disadvantage Of The Write Back And Write Through Policy In The Cache

• Write Back:

Advantage->Low latency and high throughput for write-intensive applications.

Disadvantage->There is data availability risk because cache could fail before data is persisted to backing store. This result in data being lost.

• Write Through:

Advantage->Ensures fast retrieval while making sure data is in backing store and is not lost in case the cache is disrupted.

  Disadvantage->Writing data will experience latency as we have to write to two places every time.