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

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Caching

Cache is fast (1-5 cycle access time) memory sitting between
fast registers and slow RAM (10-100 cycles access time)
Holds recently used data or instructions to save memory accesses.
Matches slow RAM access time to CPU speed if high hit rate ( $\geq 90$
Is hardware maintained and (mostly) transparent to software
Sizes range from few kB to several MB.
Usually a hierarchy of caches (2-5 levels), on- and off-chip.

Good overview in [Sch94].

Gernot Heiser 2002-08-15