[CSE]  Advanced Operating Systems 
  COMP9242 2002/S2  		UNSW
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Next: Cache mapping Up: 03-cache Previous: Cache organisation

Subsections

Cache access


Virtually indexed:
looked up by virtual address,
operates concurrently with address translation.

Physically indexed:
looked up by physical address

p-v

Cache access mechanics

  • Address is hashed to produce index of line set.
  • Associative lookup of line within set
    \(n\) lines per set: \(n\)-way set associative cache.
    • Typically \(n = 1\dots5\).
    • \(n=1\) is called direct mapped.
    • \(n=\infty\) is called fully associative, unusual for CPU caches.
  • Hashing must be simple (complex hardware is slow)
    ==> use least-significant bits of address.

Cache indexing


look

  • The tag is used to distinguish lines of set...
  • ... consists of the address bits not used for indexing.


Gernot Heiser 2002-08-15