42. What are the differences between write back and write through caches and what are the implications for system performance.

Question

What will be an ideal response?

Answer 1

When a write operation is performed to cache, the value in memory must also be modified. There are two
approaches to updating memory. If write?though is used, the cache is updated and the memory is also updated
in parallel. If write?back is implemented, the main store is not updated when the cache is accessed, but when
the cache line is flushed.

Write?back caching is generally regarded as having a higher?performance than write?through caching because
the cache to memory traffic is reduced (if a cache line is written to many times, the memory is updated only
when the line is flushed). However, write?back cache takes the risk that a system crash may result in the
modified data never being written back to main store.