L9-1 - ELEC152 Computer Organization Lecture 9: Memory...

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ELEC152 Computer Organization Lecture 9: Memory Hierarchy Professor George Yuan Office: Rm. 2527 Email:eeyuan@ust.hk
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The Five Classic Components of a Computer rocessor Processor Input Control Memory Datapath Output ELEC152 Computer Organization Spring 2009 Page 2
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Technology Trends Capacity Speed Logic: 2x in 3 years 2x in 3 years DRAM: 4x in 3 years 2x in 10 years Disk: 4x in 3 years 2x in 10 years RAM DRAM Year Size Cycle Time 1980 64 Kb 250 ns 983 56 Kb 20 ns 1983 256 Kb 220 ns 1986 1 Mb 190 ns 1989 4 Mb 165 ns 992 6 Mb 45 ns 1992 16 Mb 145 ns 1995 64 Mb 120 ns 2003 1Gb 20ns ELEC152 Computer Organization Spring 2009 Page 3
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Who Cares About the Memory Hierarchy? Processor-DRAM Memory Gap (latency) Proc 000 μProc 60%/yr. (2X/1.5yr) 1000 CPU nce “Moore’s Law” 0 100 Processor-Memory Performance Gap: (grows 50% / year) forma n DRAM 9%/yr. 10 DRAM Per f (2X/10 yrs) 1 1980 1981 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 1982 ELEC152 Computer Organization Spring 2009 Page 4 Time
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Today’s Situation: Microprocessor Rely on caches to bridge gap Microprocessor-DRAM performance gap time of a full cache miss in instructions executed 1st Alpha (7000): 340 ns/5.0 ns = 68 clks x 2 or 136 instructions 2nd Alpha (8400): 266 ns/3.3 ns = 80 clks x 4 or 320 instructions 3rd Alpha (t.b.d.): 180 ns/1.7 ns =108 clks x 6 or 648 instructions p( ) 1/2X latency x 3X clock rate x 3X Instr/clock -5X ELEC152 Computer Organization Spring 2009 Page 5
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The Goal: illusion of large, fast, cheap memory Fact: Large memories are slow, fast memories are small How do we create a memory that is large, cheap and fast (most of the time)? Hierarchy Parallelism An Expanded View of the Memory System Control Processor Datapath Memory Mem o Memory Memory ry Fastest Slowest Smallest Biggest Speed: Size: ELEC152 Computer Organization Spring 2009 Page 6 Highest Lowest Cost:
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Exploiting Memory Hierarchy Users want large and fast memories! SRAM access times are 1 - 15ns at cost of $20 to $80 per Mbyte. RAM access times are 20- 0ns at cost of $0.5 to $2 per Mbyte. DRAM access times are 20 60ns at cost of $0.5 to $2 per Mbyte. Disk access times are 5 to 10 million ns at cost of $.010 to $.020 per Mbyte. ry and give it to them anyway CPU Try and give it to them anyway build a memory hierarchy Level 1 Increasing distance om the CPU in Level 2 Levels in the memory hierarchy access time Level n ELEC152 Computer Organization Spring 2009 Page 7 Size of the memory at each level
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Memory Hierarchy of a Modern Computer System By taking advantage of the principle of locality: Present the user with as much memory as is available in the cheapest technology. rovide access at the speed offered by the fastest technology Provide access at the speed offered by the fastest technology. rocessor Control Secondary Processor Tertiary torage Datapath Storage (Disk) Regist e Main Memory (DRAM) Second Level Cache RAM) On-Ch i Cach Storage (Disk) rs (SRAM) ip s 0,000,000s peed (ns): 0s 00s 0,000,000,000s ELEC152 Computer Organization Spring 2009 Page 8 1s 10,000,000s (10s ms) Speed (ns): 10s 100s 100s Gs Size (bytes): Ks Ms 10,000,000,000s (10s sec) Ts
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Principle of Locality principle that makes having a memory hierarchy a good idea
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L9-1 - ELEC152 Computer Organization Lecture 9: Memory...

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