Sectored (or subblock) Caches

• First cache ever (IBM 360/85 in late 60’s) was a sector cache

  • On a cache miss, send only a subblock, change the tag and invalidate all other subblocks
  • Saves on memory bandwidth

• Reduces number of tags but requires good spatial locality in application

• Requires status bits (valid, dirty) per subblock

• Might reduce false-sharing in multiprocessors

  • But requires metadata status bits for each subblock
  • Alpha 21164 L2 uses a dirty bit/16 B for a 64B block size

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