Sectored (or subblock) caches
First cache ever (IBM 360/85 in late 60’s) was a sector cache
Reduce number of tags but requires good spatial locality in application
Requires status bits (valid, dirty) per subblock (also for cache coherence).
- Alpha 21164 L2 uses a dirty bit/16 B for a 64B block size
Can also be done as a variation on write policy (write validate): no fetch-on write but write allocate