Select a Memory Divider and Set Some Timings

The latest generation of Intel memory controllers provides a much more expansive choice in memory dividers than ever before. That said, there are only three that we ever use, the most obvious of these being 1:1. Setting 1:1, simply put, means that the memory runs synchronously with the FSB. Keep in mind though that the FSB is quad-pumped (QDR) and memory is double data rate (DDR). For example, setting an FSB of 400MHz results in a 1.6GHz (4 x 400) effective FSB frequency at DDR-800 (2 x 400), assuming your memory is running 1:1. Selecting 5:4 at an FSB of 400MHz sets a memory speed of DDR-1000 (5/4 x 2 x 400). The other two dividers we would consider using besides 1:1 are 5:4, and in the case of DDR3, 2:1.

Regrettably, there are rarely any real performance gains by moving to memory ratios greater than 1:1. While it is true that many synthetic benchmarks will reward you with higher read and copy bandwidth values, the reality of the situation is that few programs are in fact bottlenecked with respect to total memory throughput. If we were to take the time to analyze what happens to true memory latency when moving from DDR2-800 CAS3 to DDR2-1000 CAS4, we would find that overall memory access times might actually increase. That may seem counterintuitive to the casual observer and is a great example of why it's important to understand the effect before committing to the change.

Start your next phase of tuning by once again entering the BIOS and selecting a memory divider. As mentioned earlier, even though there are many choices in dividers you will do best to stick to either 1:1 or 5:4 when using DDR2 and 2:1 when running DDR3. Next set your primary timings - typically, even the worst "performance" memory can handle CAS3 when running at about DDR2-800, CAS4 to about DDR2-1075, and CAS5 for anything higher. These are only approximate ranges though and your results will vary depending on the design of you motherboard's memory system layout, the quality of your memory, and the voltages you apply. You may find it easiest to set all primary memory timings (CL-tRCD-tRP) to the same value when first testing (i.e. 4-4-4, 5-5-5, etc.), and as a general rule of thumb, cycle time (tRAS) should be set no lower than tRCD + tRP + 2 when using DDR2 - for DDR3 try to keep this value between 15 and 18 clocks inclusive.

Failure of the board to POST (Power On Self-Test) after adjusting memory settings is a strong indication that either: A) you've exceed the memory's maximum possible frequency - choose a divider that results in a lower memory speed; B) the timings are too tight (low) for the attempted speed - loosen the values and try again; or C) the particular frequency/timing combination is possible, but not at the voltage currently applied - raise the memory voltage. Not all failure to POST conditions will have a solution. Some motherboards simply refuse to run certain memory dividers and we're finding more and more memory modules these days that are just flat out incapable of running the tighter timings possible with the previous generation's products.

Booting to the Windows desktop is always a pretty good indication that you are at least close to final stable values when it comes to memory. Again, start Prime95 and run at least 30 minutes of the blend test. Failures, especially rounding errors, are strong indications of memory problems. If you encounter errors, reset the system and increase the memory voltage by a small amount, always remembering to stay within specified limits. If you continue to experience errors, regardless of memory voltage, then you should loosen the primary timings and continue the testing. Once you have managed to "prime" for 30 minutes or more you can move on to the final phase - overclocking the CPU.

Tuning Memory Subsystem Performance Overclock That CPU
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  • mariedeguzman - Friday, June 19, 2009 - link

    Thanks for this post, this is a great article and a good help to those who need advices about this post.
  • Markfw900 - Thursday, January 10, 2008 - link

    My Gigabyte P35-DQ6 does have what you say is voffset, but is has NO vdroop from idle to load. I believe this is because it has a far superior power delivery system. I don't have an instrument to tell me any differences that may happen in nano-seconds on the voltage, but overall, it never seems to change. This would be consistant with a high quality board. So why do you say its a feature ? I can see how a mfg may undervolt to not go over recommended vcore for non-overclocked cpu's, but if I didn't overclock, my board wouldn't have vdroop either.

    Its just cheap motherboards, not a "feature". If I am wrong, please test a DQ6 and show the results.
  • LaGUNaMAN - Saturday, January 5, 2008 - link

    One of the best tech articles I've read in awhile. (^^,)
  • isvaljek - Tuesday, January 1, 2008 - link

    "typically, even the worst "performance" memory can handle CAS3 when running at about DDR2-800, CAS4 to about DDR2-1075, and CAS5 for anything higher."

    Are they for real?
  • mindless1 - Monday, December 31, 2007 - link

    Considering the heat produced I can't see a justification for the idea of drastic shifts in the cooling industry. Realistically there aren't THAT many overclockers using water cooling at all and current (including older) processors having lower power consumption were what brought the cooling industry to what it is today.

    You may say past some point the heat isn't the factor, but you still need a decent heatsink up until that point. 100W of heat for example is a non-trivial level even though some past parts have exceeded that.
  • mindless1 - Monday, December 31, 2007 - link

    What I really meant to say is that it's not just a matter of getting rid of the heat but doing so without the system sounding like it has a leaf blower hidden inside, and for that many lesser heatsinks just don't cut it.
  • mindless1 - Monday, December 31, 2007 - link

    What I really meant to say is that it's not just a matter of getting rid of the heat but doing so without the system sounding like it has a leaf blower hidden inside and for that many lesser heatsinks just don't cut it.
  • mindless1 - Monday, December 31, 2007 - link

    What I really meant to say is that it's not just a matter of getting rid of the heat but doing so without the system sounding like it has a leaf-blower hidden inside and for that many lesser heatsinks just don't cut it.
  • SilthDraeth - Friday, December 21, 2007 - link

    And their TDP measurement is the same as it has always been, maximum draw.

    Yes ACP is a marketing tool. So what. MHZ is a marketing tool as well, and still has real world benefits. Same as ACP.

  • wordsworm - Thursday, December 20, 2007 - link

    Best damned article I've seen out of AT in a long time. Bravo.

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