We have been testing the overclocking capabilities of the Phenom II X4 940 (seriously, who names these products?) for an AMD roundup and have hit the proverbial brick wall. It has not been for the lack of trying or even using a stellar motherboard to test these processors. The motherboard choices have ranged from some wicked little 790GX overclockers from ASRock, Gigabyte, and DFI to the flagship 790FX products from ASUS, MSI, and Foxconn. We even tried a few NVIDIA 780a based motherboards along with a slew of newly arrived AM3 compatible boards. We changed cooling, processors, video cards, disk drives, memory, and tried every available voltage setting. It did not matter. We could not break the 4GHz barrier and still complete our benchmark test suite.

The only commonality between our 30 different setups is the operating system. We recently standardized on Vista Ultimate 64 SP1 for testing. Granted, we had this same problem when our 940 engineering samples first arrived and we asked AMD about it. However, AMD never did get to the bottom of it before the launch date. We thought our results might change with retail processors. Alas, they did not. We have four retail CPUs, three with 0850 lot codes and one from the 0849 batch that all behave the same way under Vista 64.

Our final benchmark stable clock speed is 3.955GHz reached via a 17.5 core multiplier and a 226 HTT setting on our . This required a 1.6V VCore setting (with droop, real voltage is around 1.585V) on our DFI DK 790FXB-M2RSH motherboard. Memory speed is DDR2-1205 at 5-5-5-18 timings with VDimm at 2.060V. This is the setting we will utilize in our upcoming roundups. We mention it now as our Core i7 920 will operate at 4GHz and Q9550 at 4.25GHz, not exactly fair, but we are looking at platform capabilities on air cooling in the overclocked sections. As one would say, it what it is.



What is really strange is the behavior of the OS and Phenom II X4 940 at the 4GHz mark. We actually have 3.990GHz (19x210) stable for all tests except Crysis and the PCMark Vantage TV/Movies test suite. With that in mind, a simple change to 19x211 for a 4.009GHz clock speed results in the majority of our tests failing. We sometimes have trouble even entering Vista at 19x211, while 19x210 is about 97% benchmark stable. We have tried every possible combination (20x200, memory at DDR2-800, 1GHz NB speed, etc.) and even chilled the processor down to 16C and raised processor voltages above 1.7, nothing worked above 4GHz.

At least under Vista 64 as Vista 32 was much different. The settings mentioned earlier allowed us to reach a stable 4.275GHz (19x225) with the same components. However, we are not utilizing Vista 32 in testing anymore, especially considering our standard benchmarks are completed with 4GB and 8GB configurations on the DDR2 platforms. As such, it appears at this time that any overclocking comparisons will be limited to under 4GHz on the AM2+ and AM3 platforms. We have addressed this problem with AMD again and hopefully an answer is forthcoming. In the meantime, we figured out a way to get a screenshot above 4GHz before we received the standard BSOD routine. At least it is a consolation prize at this point.




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  • DavidMMM - Sunday, February 8, 2009 - link

    the proof is here:


    probably with a better mobo and better air cooling, he can pass the 4GHz barrier air cooled.
  • Jayw - Thursday, February 5, 2009 - link

    Gosh Almighty...It's the memory controler. How a 64 bit OS and a 32 bit OS deal with mem..verses the mem controler on the processor..

    Thats just my humble opinion. Iam still weighting the benifits of 64 bit and speed is always the prime consideration.
  • stainremover - Monday, February 2, 2009 - link

    just a suggestion, but have you tried using amd overdrive to overclock? all those videos of the 3dmark world record @ 6.5ghz involve using amd overdrive... Reply
  • jmurbank - Monday, February 2, 2009 - link

    Let us get some things straight. One AMD K8 and K10 processors have enough memory bandwidth to start out with. K8 and K10 have issues with latency, so it is better to lower the timings for better performance. Over clocking the memory gains nothing for these processors. When over clocking processors, the path ways and transistors starts oscillating. Over clocking requires higher quality power to go further. Probably the best way to do a good over clock is use a oscilloscope and check the quality of both the power supply unit and power supply in the motherboard.

    If the Phenom II processor can not handle past 4 GHz, then it could either be its built-in power circuitry that may not be enough to power the processor at this speed or the quality of the transistors and pathways are not at a high enough quality. If it is possible, turning off one or two cores to gain back the ability to over clock the processor further. If it can the power grid is a little under designed or the transistors can not handle very hot temperatures at a high speeds. If want all four cores to be over clocked, super cooling may have to be done.

    I prefer AMD because a total system build is cheaper compared to Intel. Intel is OK and costly if you want a pristine 80x86 processor straight from a company that invented this type of processor. I can care less about over clocking.

    Windows users crying over Vista that they can not over clock their processor as far any more need to think of something else. Over clocking and using GNU/Linux will not provide a reliable setup and it never has. GNU/Linux uses system resources more efficiently or uses the system to near 99% to do tasks and it finishes faster. Windows Vista does a lot of stuff and it goes slow, so you think over clocking might compensate for the lost of performance.
  • Goty - Sunday, February 1, 2009 - link

    It's well documented that Vista is much tougher on CPU overclocks than XP was (same with going from 98 to XP), and it's no secret that moving to a 64-bit operating system has much the same effect.

    I don't see why you're so confused that your overclocking headroom goes down when going to Vista x64. When you start getting into those extra registers, you've got more points of possible failure, so naturally it's going to be harder to get an overclock stable.
  • haukionkannel - Sunday, February 1, 2009 - link

    Well you are right that in that list none of them got over 4GHz using air. On the other hant PhenomII seems to like cold, so estimations about some hotspots in 64 code execution can be real. In that list there was 4.3 with 64 bit with TEC cooling. So there is more potential. We need new stepping to achieve it with air though. Reply
  • Murphy9090 - Sunday, February 1, 2009 - link

    Well glad to see a good argument? Blows chunks really, then the Q9400 Q9550 must blow chunks by your so eloquent statement. Considering they are similar in price and speed.

    I was trying to clear some images up about the Phenom 2 and we get "blows chunks." Great choice or words, and your bashing the other idiot on these comments. I'm not a fan boy. by no means. and have no problem switching from one company to the other. Instead of watching apples to oranges comparisons, lets compare apples to say um maybe apples. Or even get close with applesauce
  • Murphy9090 - Saturday, January 31, 2009 - link

    Hey this is coming from the same guys that used the excuse of using a pretty crappy Heatsink on the comparison between the i7 and the Phenom 2. Their excuse: It was the only one available that was Phenom 2 ready. Amazing considering its an AM2+ part and the only thing that changed was a die shrink and some streamlining.

    One other thing, the AMD 940 was never designed to go up against the i7, period, end of story.

    Glad to see another Anandtech article whining about how bad there overclocks are when they could only pull 2.9 ghz on an original Phenom, w/ the new 750SB motherboards. Check out some forums to learn how to overclock. And try using the same coolers to compare products so your biased doesnt shine through yalls blue tinted lenses
  • Murphy9090 - Saturday, January 31, 2009 - link

    Correction: My apologies Anandtech didnt do the article w/ the crappy cooler, that would be another AMD bashing site"TH". But I will stick by my arguement of the AMD Phenom 2 940 never being developed to compete with a brand new product like the i7. Also the guys saying AMD needs to shut there doors, roflol. The only reason you can get your intel chips at the prices your paying is because of AMD's competition in the market. Wish for AMD's demise and watch Intel run away w/ your wallet.

    As others have stated, please try w/ a different X64 operating system and get back to us. AS most of us have come to realize that Vista has some strange tendencies.
  • 0vercl0ck - Saturday, January 31, 2009 - link

    Murphy 9090,

    You got that one right baby!

    They are overclockers want to be!

    Once one try AMD, the real man will never go back to InHell in sLide.

    i7 is a microwave oven, not a CPU!

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