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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

Cache types

• Virtually indexed, virtually tagged (also called virtual cache):
  • only uses virtual addresses,
  • can operate concurrently with MMU.

• Virtually indexed, physically tagged:
  • virtual address for accessing line, physical address for tagging,
  • needs address translation completed for retrieving data,
  • index concurrently with MMU, use MMU output for tag check.

• Physically indexed:
  • only uses physical addresses
  • needs address translation completed before begin of access

• Typically, virtually indexed caches are on-chip, physically indexed caches are off-chip.