[ The PC Guide | Systems and Components Reference Guide | Motherboard and System Devices | System Cache | Cache Characteristics ]

Write Policy

The cache's write policy determines how it handles writes to memory locations that are currently being held in cache. Described in more detail here, the two policy types are:

• Write-Back Cache: When the system writes to a memory location that is currently held in cache, it only writes the new information to the appropriate cache line. When the cache line is eventually needed for some other memory address, the changed data is "written back" to system memory. This type of cache provides better performance than a write-through cache, because it saves on (time-consuming) write cycles to memory.
• Write-Through Cache: When the system writes to a memory location that is currently held in cache, it writes the new information both to the appropriate cache line and the memory location itself at the same time. This type of caching provides worse performance than write-back, but is simpler to implement and has the advantage of internal consistency, because the cache is never out of sync with the memory the way it is with a write-back cache.

Both write-back and write-through caches are used extensively, with write-back designs more prevalent in newer and more modern machines.

Next: Transactional or Non-Blocking Cache

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