L32 - CS61C L32 Caches I Wawrzynek, Fall 2007 UCB 11/9/2007...

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Unformatted text preview: CS61C L32 Caches I Wawrzynek, Fall 2007 UCB 11/9/2007 John Wawrzynek (www.cs.berkeley.edu/~johnw) www-inst.eecs.berkeley.edu/~cs61c/ CS61C Machine Structures Lecture 31 - Caches I 1 CS61C L32 Caches I Wawrzynek, Fall 2007 UCB The Big Picture Processor (active) Computer Control (brain) Datapath (brawn) Memory (passive) (where programs, data live when running) Devices Input Output Keyboard, Mouse Display , Printer Disk, Network 2 CS61C L32 Caches I Wawrzynek, Fall 2007 UCB Memory Hierarchy Processor holds data in register fle (~100 Bytes) Registers accessed on nanosecond timescale Memory (we ll call main memory) More capacity than registers (~Gbytes) Access time ~50-100 ns Hundreds o clock cycles per memory access?! Disk HUGE capacity (virtually limitless) VERY slow: runs ~milliseconds Storage in computer systems: 3 CS61C L32 Caches I Wawrzynek, Fall 2007 UCB Motivation: Why We Use Caches (written $) Proc 60%/yr. DRAM 7%/yr. 1 10 100 1000 1980 1981 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 DRAM CPU 1982 Processor-Memory Perormance Gap: (grows 50% / year) Perormance 1989 frst Intel CPU with cache on chip 1998 Pentium III has two levels o cache on chip 4 CS61C L32 Caches I Wawrzynek, Fall 2007 UCB Memory Caching Mismatch between processor and memory speeds leads us to add a new level: a memory cache Implemented with same IC processing technology as the CPU (usually integrated on same chip): faster but more expensive than DRAM memory. Cache holds a copy of a subset of main memory. Most processors have separate caches for instructions and data. 5 CS61C L32 Caches I Wawrzynek, Fall 2007 UCB Memory Hierarchy Processor Size of memory at each level Increasing Distance from Proc., Decreasing speed Level 1 Level 2 Level n Level 3 . . . Higher Lower Levels in memory hierarchy As we move to deeper levels the latency goes up and price per bit goes down. 6 CS61C L32 Caches I Wawrzynek, Fall 2007 UCB Memory Hierarchy If level closer to Processor, it is: smaller faster subset of lower levels (contains most recently used data) Lowest Level (usually disk) contains all available data (or does it go beyond the disk?) Memory Hierarchy presents the processor with the illusion of a very...
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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 University of California, Berkeley.

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L32 - CS61C L32 Caches I Wawrzynek, Fall 2007 UCB 11/9/2007...

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