tRAS and DDR2

It made little sense to test 8 new DDR2 modules at memory timings that were less than optimal for best performance. We were able to verify quickly that the traditional CAS, Ras-to-Cas delay, and RAS Precharge timings all improved performance as timings were lowered. However, tRAS at 11 or 12 is a significant departure from the best timings that we have seen with DDR on the Intel platform - it is more like the 9 to 11 optimal tRAS seen on current AMD chipsets/processors.

To determine if 11 or 12 is the best tRAS timing for DDR2, we first ran Memtest86, a commonly used memory tool that measures memory bandwidth from a custom bootable OS. Memtest86 showed absolutely no change in memory bandwidth in the range of 4 to 15 when memory timings were fixed at 4-4-4 and only tRAS was varied.

To further check our Memtest86 results, we ran a complete series of tests with Aida 32, which is also available for free download on many shareware sites. The Aida 32 memory test module is very useful because it reports both memory Read and memory Write operations as separate results. We ran both tests and also added a Total Memory Bandwidth to offer a better comparison of the test results.

 Micron PC2-4300U - 4-4-4-tRAS
 tRAS  Aida 32
Read
 Aida 32
Write
 Aida 32
Total
4 5316 2328 7644
5 5264 2338 7602
6 5289 2341 7630
7 5289 2326 7615
8 5302 2340 7642
9 5303 2349 7652
10 5314 2344 7658
11 5303 2344 7647
12 5289 2336 7625
13 5303 2339 7642
14 5264 2334 7598
15 5289 2275 7564

As you can see clearly, over the full range of tRAS 4 to tRAS 13, there is virtually no difference in memory performance when tRAS is adjusted. While there is a slight falloff at tRAS of 14 and 15, it is still minor. We can conclude that a tRAS setting of 4 to 13 makes no difference in memory performance. Since higher tRAS settings usually mean better memory stability, we can well understand why a 12 setting is standard. For our memory tests, we chose a value of 10, which represents the upper mid-range of best performance and stability. However, we did find that some high density (1GB) memory modules that were not included in our tests performed with greatest stability at a tRAS setting of 11 or 12. Overall, we had no difficulties at tRAS 10, but there is no performance penalty when using 11 or 12, if it improves the stability of your DDR2 memory.

Specifications: DDR2 Memory Performance Test Configuration
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  • Wesley Fink - Thursday, July 8, 2004 - link

    #9 - Actually the first number was copied incorrectly and has now been fixed. The tRas 11 line on p.3 now reads 5303-2344-7647.
  • FlameDeer - Thursday, July 8, 2004 - link

    Hi Wesley, nice article. :)

    Something to change:
    At page 3, Micron PC2-4300U Table, Row tRAS 11,
    Aida 32 Total should be "7697".
  • MIDIman - Thursday, July 8, 2004 - link

    > When can we expect DDR2 for A64?

    http://www.anandtech.com/cpuchipsets/showdoc.aspx?...

    http://www.anandtech.com/cpuchipsets/showdoc.aspx?...
  • mczak - Thursday, July 8, 2004 - link

    Nice article, a real pity though there are no performance numbers for overclocked FSB only (i.e. FSB 258 / DDR2-"516"). There are some reasons to believe memory performance would also be quite a bit higher than with FSB200/DDR2-533...
  • Bozo Galora - Thursday, July 8, 2004 - link

    Another clear concise mem article by Prometheus.
  • KillaKilla - Thursday, July 8, 2004 - link

    When can we expect DDR2 for A64? Even thouthe they aren't so affected by lack of memory bandwidth...
  • rjm55 - Thursday, July 8, 2004 - link

    I am not usually that much into memory articles, but this is one of the best reviews I have seen on the new Intel architecture. It was surprising that even the budget DDR2 did 667. When will Intel be launching 667 as an "official" DDR2 speed?
  • Anemone - Thursday, July 8, 2004 - link

    VERY nice article - and informative on the limits that no one else is authoritatively reviewing. Thankyou and keep them coming!

    :)
  • skiboysteve - Thursday, July 8, 2004 - link

    or... im blind..
  • skiboysteve - Thursday, July 8, 2004 - link

    you should mention in the benchmarks which modules are DS and SS, so people dont go ape shit over poor performance of say... GEIL..

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