Memory Hierarchy: Terminology

• Hit: data appears in some block in the upper level (example: Block X)

  • Hit Rate: the fraction of memory access found in the upper level
  • Hit Time: Time to access the upper level which consists of
    RAM access time + Time to determine hit/miss
    

• Miss: data needs to be retrieve from a block in the lower level (Block Y)

  • Miss Rate = 1 - (Hit Rate)
  • Miss Penalty = Time to replace a block in the upper level +
    Time to deliver the block the processor
    

• Hit Time << Miss Penalty

Lower Level

(Memory)

Upper Level

(Cache)

To Processor

From Processor

Blk X

Blk Y

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