Overclocking Intel's New 45nm QX9650: The Rules Have Changed
by Kris Boughton on December 19, 2007 2:00 AM EST- Posted in
- CPUs
Tuning Memory Subsystem Performance
Earlier, we talked about the importance of first testing your motherboard's memory subsystem before moving to the CPU. When you think about it, the reason is clear. Encountering an error while testing blindly provides absolutely no helpful information as to the source of the problem. Since both the CPU and memory stability are dependent on the FSB it only makes sense that we remove them from the equation and first tune our motherboard at our target FSB. This is accomplished by setting the target FSB (we recommend you start at 400 MHz) in the BIOS, making certain to select a CPU multiplier which places the final processor frequency at or below the default value. Next, loosen up all primary memory timings and set the memory voltage to the modules' maximum rated value. Assuming the system is in good working order, we can now attribute all observed errors to discrepancies in the MCH settings and nothing else.
 Preparing to run Prime95's blend test for the first time |
Boot the system in Windows and launch an instance of Prime95. From the menu select "Options" then "Torture Test…" and highlight the option to run the blend test (default). Now click "OK" to start the test. The blend test mode runs larger FFT values, meaning the processor must rely heavily on the memory subsystem when saving and retrieving intermediate calculation results. Although a true test of system stability would require many hours of consecutive testing, in the interest of time let the program execute for a minimum of 30 minutes.
If you encounter no errors (and the system is indeed still running), you can consider the memory subsystem "stable" at this point. If this is not the case, exit Windows, enter the BIOS, and try slightly increasing the MCH voltage. Repeat this process until you find you can complete (at least) a 30 minute run with no errors. If for some reason you find that increasing the MCH, voltage continues to have no effect on stability, or you have reached your allowable MCH voltage limit, you may be attempting to run the MCH higher than what is achievable under stable conditions. Setting Command Rate 2N - if available in the BIOS - loosening tRD, or removing two DIMMs (if you are running four) may help. If you find modifications to those items allows for completion of an initial Prime95 test, be sure to continue the testing by reducing the MCH voltage until you find the minimum stable value before moving on.
On the other hand, if you find that you can comfortably complete testing with additional MCH voltage margin to spare then you are in a good position to dial in some extra performance. Whether or not you wish to depends on your overall overclocking goal. Generally, more performance requires more voltage; this means more heat, higher temperatures, and increased operating costs. If efficiency is your focus, you may wish to stop here and move on to the next phase in tuning. Otherwise, if performance is your only concern, decreasing tRD is a great way of improving memory bandwidth, albeit usually at the expense of a higher MCH voltage.
In the end, as long as the system is stable, you are ready to move on to the next step. The insight necessary to determine just what to change and the effect if will have on stability and performance is something that comes only with experience. We cannot teach you this and experimenting further at a later time will help you sharpen these skills.
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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