Cache write (update) policy

Treatment of store operations:
- write back: Stores update cache only,
  memory updated when dirty line is replaced (flushed).
  - Memory is inconsistent with cache.
- write through: Stores update cache and memory immediately.
  - Memory is always consistent with cache.
On store to a line not presently in cache, use:
- write allocate: allocate a cache line to the data and store,
- no allocate: store to memory and bypass cache.
Usual combinations:

write-back & write-allocate,

write-through & no-allocate.

Gernot Heiser 2002-08-15