Chapter 6, Problem 27E

a)

Program Plan Intro

Cache writes policies:

• The main purpose of the cache write policies is to determine whether the main memory block is being updated such that it maps with the cache block.
• There are two types of write policies and they are:
  • Write-through
  • Write-back

Write-through:

On every write the cache and the main memory gets updated simultaneously.

Advantage:

• Ensures the cache consistency is maintained with the main memory.

Disadvantage:

• Main memory access is required during every write.
• Every write that is made to the cache requires a new main memory access to perform the write operation and it may slow down system if all access is meant to be a write operation.

Write-back:

In write-back update is made only with the main memory blocks when the blocks of the cache are chosen to be the victim and requires to be removed.

Advantage:

• Reduced memory traffic.
• Time consumed to write information to the cache will be reduced when compared with that of the write-through policy.

Disadvantage:

• The information present in the main memory and the cache memory may not have the possibility of having a same value at the given instance of time and at cases if the process terminates before performing the write operation to the main memory there is a possibility of data being lost in the cache.

b)

Program Plan Intro

Cache writes policies:

• The main purpose of the cache write policies is to determine whether the main memory block is being updated such that it maps with the cache block.
• There are two types of write policies and they are:
  • Write-through
  • Write-back

Write-through:

On every write the cache and the main memory gets updated simultaneously.

Advantage:

• Ensures the cache consistency is maintained with the main memory.

Disadvantage:

• Main memory access is required during every write.
• Every write that is made to the cache requires a new main memory access to perform the write operation and it may slow down system if all access is meant to be a write operation.

Write-back:

In write-back update is made only with the main memory blocks when the blocks of the cache are chosen to be the victim and requires to be removed.

Advantage:

• Reduced memory traffic.
• Time consumed to write information to the cache will be reduced when compared with that of the write-through policy.

Disadvantage:

• The information present in the main memory and the cache memory may not have the possibility of having a same value at the given instance of time and at cases if the process terminates before performing the write operation to the main memory there is a possibility of data being lost in the cache.