Lecture 07-memory - 1048: Computer Organization Lecture 7...

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Lecture07 - memory hierarchy (cwliu@twins.ee.nctu.edu.tw) 7-1 1048: Computer Organization 1048: Computer 1048: Computer Organization Organization Lecture 7 Lecture 7 Exploiting Memory Exploiting Memory Hierarchy Hierarchy
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Lecture07 - memory hierarchy (cwliu@twins.ee.nctu.edu.tw) 7-2 Outline Memory hierarchy Memory hierarchy • The basics of caches • Measuring and improving cache performance • Virtual memory • A common framework for memory hierarchy
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Lecture07 - memory hierarchy (cwliu@twins.ee.nctu.edu.tw) 7-3 DRAM Year Size Cycle Time 1980 64 Kb 250 ns 1983 256 Kb 220 ns 1986 1 Mb 190 ns 1989 4 Mb 165 ns 1992 16 Mb 145 ns 1995 64 Mb 120 ns 1000:1! 2:1! Technology Trends Capacity Speed (latency) Logic: 4x in 1.5 years 4x in 3 years DRAM: 4x in 3 years 2x in 10 years Disk: 4x in 3 years 2x in 10 years
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Lecture07 - memory hierarchy (cwliu@twins.ee.nctu.edu.tw) 7-4 Proc 60%/yr. (2X/1.5 yr) DRAM 9%/yr. (2X/10 yrs) 1 10 100 1000 1980 1981 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 1982 Processor-memory performance gap: (grows 50% / year) Performance Year Moore’s Law Processor Memory Latency Gap
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7-5 Control Datapath Memory Processor RF Memory Memory Memory Fastest Slowest Smallest Biggest Highest Lowest Speed: Size: Cost: Solution: Memory Hierarchy •A n I l l u s i o n o f a large, fast, cheap memory – Fact: Large memories slow, fast memories small – How to achieve: hierarchy, parallelism • An expanded view of memory system:
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7-6 Lower Level Memory Upper Level Memory To Processor From Processor Block X Block Y Memory Hierarchy: Principle • At any given time, data is copied between only two adjacent levels: – Upper level : the one closer to the processor • Smaller, faster, uses more expensive technology –L o w e r l e v e l : the one away from the processor • Bigger, slower, uses less expensive technology •B l o c k : basic unit of information transfer – Minimum unit of information that can either be present or not present in a level of the hierarchy
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Lecture07 - memory hierarchy (cwliu@twins.ee.nctu.edu.tw) 7-7 • Principle of Locality: – Program access a relatively small portion of the address space at any instant of time – 90/10 rule : 10% of code executed 90% of time •T w o t y p e s o f l o c a l i t y : – Temporal locality : if an item is referenced, it will tend to be referenced again soon – Spatial locality : if an item is referenced, items whose addresses are close by tend to be referenced soon Probability of reference address space 02 n -1 Why Hierarchy Works?
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Lecture07 - memory hierarchy (cwliu@twins.ee.nctu.edu.tw) 7-8 Tertiary Storage (Disk) Control Datapath Secondary Storage (Disk) Processor Registers Second Level Cache (SRAM) Main Memory (DRAM) On-Chip Cache 1‘s 10,000,000‘s (10’s ms) Speed (ns): 10‘s 100‘s 100‘s G’s Size (bytes): K’s M’s 10,000,000,000‘s (10’s sec) T’s How Does It Work? • Temporal locality: keep most recently accessed data items closer to the processor • Spatial locality: move blocks consists of contiguous words to the upper levels
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Lecture07 - memory hierarchy (cwliu@twins.ee.nctu.edu.tw) 7-9 CPU Registers 100s Bytes <10s ns Cache K Bytes 10-100 ns $.01-.001/bit Main Memory M Bytes
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This note was uploaded on 08/23/2009 for the course DEE 4641 taught by Professor Cwliu during the Fall '08 term at National Chiao Tung University.

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Lecture 07-memory - 1048: Computer Organization Lecture 7...

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