Overclocking Intel's New 45nm QX9650: The Rules Have Changed
by Kris Boughton on December 19, 2007 2:00 AM EST- Posted in
- CPUs
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.
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Kougar - Thursday, December 20, 2007 - link
This was the exact type of article I love to sit down and read through. It doesn't matter if portions of it are above my head, it just gets me to rise up another level to grab at them. Your article was a great read and I very much hope to see many more like this one in the future!Regarding the P5E3, I am somewhat surprised that 0.81v was the lowest you could set. Even the budget board P31-DS3L offers 0.51v as an option, my personal P35-DQ6 has 0.50v as a vCore option. I found your commentary regarding Load Line Calibration to be illuminating... this is exactly what enthusiasts like myself and others need to know.
Lastly, I hate to ask here but Google was no help, Intel's ARK database didn't cover it, and Intel's datasheet didn't mention that I could see... what exactly is P35's process size and default vCore? The same as X38's...? As much as I love Gigabyte they are notorious for their lack of system voltage info...
kjboughton - Thursday, December 20, 2007 - link
The P35 and X38 chipsets are both made using Intel's standard 90nm process technology. It's not uncommon for chipset's to lag behind current CPU offerings by a whole process generation or more. With that being said, Intel's upcoming P45 chipset, the last of it's kind (recall that all future CPU technologies will make use of an onboard memory controllers) will be made on the 65nm process -- something even the X48 won't have. In fact, this reduction in process size may have considerable benefits for P45 when it comes to the reduction in power consumption and increased performance headroom, particularlly when overclocking. The P45 default Vmch is 1.15V, X38 is slightly higer at 1.25V. Based on this I would expect to see the P45 come in around 1.05V or possibly even lower.myocardia - Thursday, December 20, 2007 - link
Kris, great article. But, when did $400-500 worth of watercooling equipment become so commonplace, as to be putting the one (or is that two?) companies who make phase-change units out of business? If freon is no longer needed for extreme CPU cooling, couldn't Vapochill just start making even more expensive, higher-end watercooling?spamme33 - Thursday, December 20, 2007 - link
I have been overclocking since my first computer build years and years ago, rarely do I learn that much from one article. Very well written, informative, and timely!kilkennycat - Thursday, December 20, 2007 - link
The documentation accompanying the BIOS settings of almost all enthusiast motherboards is frequently obscure and incomplete - probably because it is printed many months before the board/BIOS is released, plus the leading manufacturers never bother to update BIOS user-documentation when they update the BIOS. Also, it does seem that the documentation authors have a uniformly poor grasp of the English language and prefer to keep descriptions of all BIOS settings as vague and incomprehensible as possible. It is also so common to find sundry BIOS entries not documented AT ALL anywhere in the motherboard manual, even the (so-called) latest on-line version.So I have a request on behalf of those like myself desperately trying to understand each entry in the BIOS of that brand-new and very expensive enthusiastic motherboard that I have just purchased, with that abysmal so-called user-manual and pathetic in-BIOS "Help" Function-key :-
Would it be possible for you or other at Anandtech to fully document/explain all the terms used in the text of the CPU and memory BIOS settings of the most popular enthusiast motherboards?
To keep such an exercise manageable, I suggest confining the exercise initially to existing and upcoming enthusiast desktop motherboards that are fully compatible with Penryn and Phenom. At present, X48, nVidia 780i, AMD 790FX.....
poohbear - Thursday, December 20, 2007 - link
thank you very much for such an informative and detailed article. very much appreciated for us overclockers and the future looks fantabulous w/ these cpus.wyemarn - Thursday, December 20, 2007 - link
Thank you very much for this great article. What a wonderful Christmas gift from Anandtech! This is one the most complete article I have ever read. CPU performance, overclocking, mobo settings, power consumption all in one article. What a joy to read.akaevile - Thursday, December 20, 2007 - link
Thank you for the detailed information. One has to be a little nervous however for the implications in what your work has found. Will Intel's improvements in refining 45nm technology push the line or has it been drawn in the sand??n7 - Wednesday, December 19, 2007 - link
Really superb article.Possibly the best i've ever seen on AT!
Thanx for the indepth info!
Bozo Galora - Wednesday, December 19, 2007 - link
looks like not only the X48, but three 45nm quads also will be delayed - due to AMD incompetence.http://www.digitimes.com/mobos/a20071218PD212.html">http://www.digitimes.com/mobos/a20071218PD212.html