DDR2 Ram Question
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From: Joe on 20 Jul 2006 19:54 What would be the appropriate speed Ram for a X2 3800 or X2 4600? Can you use 533 or 800? If so is there much difference? What has changed from the Socket A days? It seems like you used to have to get ram of a speed to match your CPU or if you did not you would either be really overclocking your Ram or underclocking your CPU. I have not upgraded in about two years so I am a bit behind hear please help. Joe
From: Paul on 21 Jul 2006 03:45
In article <fIUvg.22074$cu1.2337(a)bignews3.bellsouth.net>, "Joe" <nospam(a)bellsouth.net> wrote: > What would be the appropriate speed Ram for a X2 3800 or X2 4600? Can you > use 533 or 800? If so is there much difference? What has changed from the > Socket A days? It seems like you used to have to get ram of a speed to match > your CPU or if you did not you would either be really overclocking your Ram > or underclocking your CPU. I have not upgraded in about two years so I am a > bit behind hear please help. > > Joe Start with Table 4 on PDF page 33: http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/32559.pdf 200-MHz (DDR2-400) PC2-3200 DIMMs 266-MHz (DDR2-533) PC2-4200 DIMMs 333-MHz (DDR2-667) PC2-5300 DIMMs 400-MHz (DDR2-800) PC2-6400 DIMMs Multiplier Core DRAM Frequency Frequency 200MHz 266MHz 333MHz 400MHz 4 800MHz 160.00 160.00 160.00 160.00 5 1000MHz 200.00 200.00 200.00 200.00 6 1200MHz 200.00 240.00 240.00 240.00 7 1400MHz 200.00 233.33 280.00 280.00 8 1600MHz 200.00 266.67 320.00 320.00 9 1800MHz 200.00 257.14 300.00 360.00 10 2000MHz 200.00 250 333.33 400.00 11 2200MHz 200.00 244.44 314.29 366.67 12 2400MHz 200.00 266.67 300.00 400.00 13 2600MHz 200.00 260.00 325.00 371.43 14 2800MHz 200.00 254.55 311.11 400.00 15 3000MHz 200.00 250.00 333.33 375.00 So speeds up to DDR2-800 are supported for any processor, in the sense that they will run. But notice some of the limitations, in terms of the clocks provided for the DIMMs. First off, the multiplier is multiplied by the nominal 200MHz processor clock. That gives the core freq in the next column. The core frequency is then divided by a programmable memory divider. Notice that when the core runs at 800MHz, the memory divider won't go any lower than 5. The highest memory divider seems to be 15. You can always get the worth of the memory, by raising the CPU clock above its 200MHz nominal value. So if your DDR2-800 memory was receiving a 360MHz clock instead of the 400MHz it would normally get, you could increase the FSB clock to 200*(400/360)=222MHz. Of course, your core is also overclocked by 11% when you do that, but then the memory is running at full speed. As for latency, you can look at these articles: Latency values (table) - DDR2-800 4-4-4 is the same as DDR400 2-2-2 So to win on latency alone, a DDR2-800 3-3-3 type memory would be needed. In practice that is not necessary (DDR2-800 5-5-5 is good enough). http://www.xbitlabs.com/articles/memory/display/ddr2-ddr_3.html Latency measured - http://www.xbitlabs.com/articles/cpu/display/amd-socket-am2_11.html The SuperPI results suggest the DDR2-800 5-5-5 is good enough - http://www.xbitlabs.com/articles/cpu/display/amd-socket-am2_12.html Applications results (Photoshop CS 2) - Tomshardware is a bit different I don't know why the DDR400 2-2-2 is winning here. http://www.tomshardware.com/2006/05/23/amd_reinvents_itself/page37.html Looking at prices, there doesn't appear to be too much of a premium going from 5-5-5 to 4-4-4 (just stay away from modules with flashing LEDS on them). So the 4-4-4 are within reach, but do you get enough benefit to be bothered ? Anything faster than 4-4-4 appears to be madness. BTW - this is not a comprehensive review of all the AM2 benchmarks out there, or for that matter, even a correct conclusion. Since you are buying this thing, it wouldn't hurt to dig up a few more reviews and come up with your own conclusions. Note - some of the memories state a voltage requirement for the stated clock rate and timing values. Make sure the motherboard has adjustable DIMM voltage, to keep a premium memory happy. And for some reason, some of the DDR2 state "Intel only", and I haven't heard a story as to why that would be. Paul |