Tuesday, January 27, 2009

memory hierarchy

cost size distance speed
registers $$$ 32 bytes in the room 1cycle(afew ns)
cache $$ a few MB next door cycles(10's ns)
main memory $ GB hall 100s of ns
disk c GB 100 miles a few ms

that are built into the CPU are generally accessible within one cycle of the CPU clock. Main memory is accessed via a transaction on the memory bus, and it may take many cycles of CPU clock. Cache is a memory buffer used to accommodate a speed differential.

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