ch3-memory-io-1-hierarchy

ch3-memory-io-1-hierarchy - 3-1: Memory Hierarchy3-1:...

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Unformatted text preview: 3-1: Memory Hierarchy3-1: Memory HierarchyProf. Mikko H. LipastiUniversity of Wisconsin-MadisonCompanion Lecture Notes for Modern Processor Design: Fundamentals of Superscalar Processors, 1stedition, by John P. Shen and Mikko H. LipastiTerms of use: This lecture is licensed for non-commercial private use to anyone that owns a legitimate purchased copy of the above-mentioned textbook. All others must contact mikko@engr.wisc.edufor licensing terms. 2005 Mikko Lipasti2Memory HierarchyMemory HierarchyMemoryJust an ocean of bitsMany technologies are availableKey issuesTechnology (how bits are stored)Placement (where bits are stored)Identification (finding the right bits)Replacement (finding space for new bits)Write policy (propagating changes to bits)Must answer these regardless of memory type 2005 Mikko Lipasti3Types of MemoryTypes of MemoryTypeSizeSpeedCost/bitRegister< 1KB< 1ns$$$$On-chip SRAM8KB-6MB< 10ns$$$Off-chip SRAM 1Mb 16Mb< 20ns$$DRAM64MB 1TB< 100ns$Flash64MB 32GB< 100uscDisk40GB 1PB< 20ms~0 2005 Mikko Lipasti4Memory HierarchyMemory HierarchyRegistersOn-ChipSRAMOff-ChipSRAMDRAMFlash/DiskCAPACITYSPEED and COST 2005 Mikko Lipasti5Bandwidth:Capacity:1+GB for Windows PC to multiple TBCost:(TB x anything) adds up quicklyThese requirements appear incompatibleWhy Memory Hierarchy?Why Memory Hierarchy?sec6.21sec384.41.1GBGcyclesDrefBinstDrefIfetchBinstIfetchcycleinstBW=+= 2005 Mikko Lipasti6Why Memory Hierarchy?Why Memory Hierarchy?Fast and small memoriesEnable quick access (fast cycle time)Enable lots of bandwidth (1+ L/S/I-fetch/cycle)Slower larger memoriesCapture larger share of memoryStill relatively fastSlow huge memoriesHold rarely-needed stateNeeded for correctnessAll together: provide appearance of large, fast memory with cost of cheap, slow memory 2005 Mikko Lipasti7Why Does a Hierarchy Work?Why Does a Hierarchy Work?Locality of referenceTemporal localityReference same memory location repeatedlySpatial localityReference near neighbors around the same timeEmpirically observedSignificant!Even small local storage (8KB) often satisfies >90% of references to multi-MB data set 2005 Mikko Lipasti8Memory HierarchyMemory HierarchyCPUI & D L1 CacheShared L2 CacheMain MemoryDiskTemporal Locality Keep recently referenced items at higher levels Future references satisfied quicklySpatial Locality Bring neighbors of recently referenced to higher levels Future references satisfied quickly 2005 Mikko Lipasti9Four Key IssuesFour Key IssuesThese are:PlacementWhere can a block of memory go?...
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This note was uploaded on 03/02/2012 for the course ECE 752 taught by Professor Profgurisohi during the Spring '09 term at Wisconsin.

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ch3-memory-io-1-hierarchy - 3-1: Memory Hierarchy3-1:...

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