rs6 - EE108B Review Session #6 Daxia Ge Friday February...

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EE108B Review Session #6 Daxia Ge Friday February 23 rd , 2007
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Cache Review - 2 Today’s Menu: Announcements Cache Review Intro Cache organizations Mechanics (Index, Tag, etc.) Design Choices Examples HW Hints
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Cache Review - 3 Review: The Memory Problem We need: Big , fast , cheap memory But: Big memories are slow Even when built from fast components Fast memories are expensive and small
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Cache Review - 4 We Are Lucky: Programs Have Locality! Principle of Locality Programs access a relatively small portion of the address space at any given time Can tell what memory locations a program will reference in the future by looking at what it referenced recently in the past Two Types of Locality Temporal Locality - If an item has been referenced recently, it will tend to be referenced again soon Spatial Locality - If an item has been referenced recently, nearby items will tend to be referenced soon • Nearby refers to memory addresses
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Cache Review - 5 The Solution Memory can be arranged as hierarchies The goal is to provide the illusion of lots of fast memory But how do you manage this, and make it work? Control Datapath Memory Processor Memory Memory Memory Fastest Slowest Smallest Biggest Highest Lowest Speed: Size: Cost:
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Cache Review - 6 Designing Caches Organization: Direct Mapped Set Associative Fully Associative Design Choices: Block size Replacement Policy Write back/Write through Write Miss/Fetch Policy Others: consistency, etc?
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Cache Review - 7 Direct Mapped Cache 16 Word Memory 4 Word Direct Mapped Cache Memory Address 0 1 2 3 4 5 6 7 8 9 A B C D E F Cache Index 0 1 2 3
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Cache Review - 8 Set Associative Cache 4 Word 2 Way Set Associative Cache Memory Address 0 1 2 3 4 5 6 7 8 9 A B C D E F Cache Index 0 1 0 1 16 Word Memory
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rs6 - EE108B Review Session #6 Daxia Ge Friday February...

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