L35 - CS61C Machine Structures Lecture 35 Virtual Memory I...

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CS61C L35 Virtual Memory I Wawrzynek, Fall 2007 © UCB 11/19/2007 John Wawrzynek (www.cs.berkeley.edu/~johnw) www-inst.eecs.berkeley.edu/~cs61c/ CS61C – Machine Structures Lecture 35 - Virtual Memory I 1 CS61C L35 Virtual Memory I Wawrzynek, Fall 2007 © UCB Review: Caches Cache design choices: • size of cache: speed v. capacity • direct-mapped v. associative • for N-way set assoc: choice of N • block replacement policy • 2nd level cache? • Write through v. write back? Best choice depends on programs, technology, budget. Use performance model to pick between choices. 2
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CS61C L35 Virtual Memory I Wawrzynek, Fall 2007 © UCB Another View of the Memory Hierarchy Regs L2 Cache Memory Disk Tape Instr. Operands Blocks Pages Files Upper Level Lower Level Faster Larger Cache Blocks Thus far { { Next: Virtual Memory 3 CS61C L35 Virtual Memory I Wawrzynek, Fall 2007 © UCB Memory Hierarchy Requirements If Principle of Locality allows caches to offer (close to) speed of cache memory with size of DRAM memory, then recursively why not use at next level to give speed of DRAM memory, size of Disk memory? While we ʼ re at it, what other things do we need from our memory system? 4
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CS61C L35 Virtual Memory I Wawrzynek, Fall 2007 © UCB Memory Hierarchy Requirements Allow multiple processes to simultaneously occupy memory and provide protection – don ʼ t let one program read/write memory from another Address space – give each program the illusion that it has its own private memory • Suppose code starts at address 0x40000000. But different processes have different code, both residing at the same address. So each program has a different view of memory. 5 CS61C L35 Virtual Memory I Wawrzynek, Fall 2007 © UCB Virtual Memory Called “ Virtual Memory Next level in the memory hierarchy: • Provides program with illusion of a very large main memory: • Working set of “pages” reside in main memory - others reside on disk. Also allows OS to share memory, protect programs from each other Today, more important for protection vs. just another level of memory hierarchy Each process thinks it has all the memory to itself 6
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CS61C L35 Virtual Memory I Wawrzynek, Fall 2007 © UCB Virtual to Physical Address Translation Each program operates in its own virtual address space; ~only program running Each is protected from the other
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This note was uploaded on 04/09/2008 for the course CS 61A taught by Professor Harvey during the Spring '08 term at Berkeley.

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L35 - CS61C Machine Structures Lecture 35 Virtual Memory I...

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