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Cache-Memory Coherence
Figure 4.6:
Write-Through vs. Write-Back.
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- In a single cache system, coherence between memory and the cache is maintained using one of two policies:
- write-through,
- write-back (see Fig. 4.6).
- When a task running on a processor P requests the data in memory location X, for example, the contents of X are copied to the cache, where it is passed on to P.
- When P updates the value of X in the cache, the other copy in memory also needs to be updated in order to maintain consistency.
- In write-through, the memory is updated every time the cache is updated,
- while in write-back, the memory is updated only when
the block in the cache is being replaced.
Cem Ozdogan
2006-12-27