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AMD Phenom II X4 940 Overclocking

With various motherboards. How it affects games.

March 2, 2009



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AMD has updated its gaming platform codenamed Dragon with launching Phenom II processors. Note that we have already reviewed some parts of this platform (for example, AMD 790GX Chipset, AMD 770/790 Chipsets, ATI RADEON 4850 512MB, AMD Phenom II X4 940 Processor). As all these parts turned out to be much more attractive than competitors in our tests and in terms of features, it's logical to assume that the new platform will merge all advantages of its constituent parts not just to make a poor part look better at the cost of other elements, but to raise platform attractiveness to a new level. Indeed, the Dragon platform has all chances for success, and it can boast of initially democratic prices, which is an important thing in these days of crisis.



However, in this article we'll leave out economic issues and phrases like "Wow, the entire computer is less than $1000". We'll deal only with technical issues of the platform as a whole. Let's see how Phenom II overclocks on various motherboards, as it's the gaming platform where it makes most sense (if you use your computer for serious tasks, it may just as well work for several hours, it's stability that matters; if you need your results much faster, you should think about a multi-CPU workstation or optimize your computational tasks). Then we'll figure out performance gains from moderate overclocking in modern games (that is how you overclock your computer without much efforts and extra investments into hardware).

Brief theory

As is well known, the first models of Phenom II can be installed on motherboards with Socket AM2+. But as they have TDP of 125W, we should certainly stick to motherboards with corresponding VRMs. By the way, it does not mean that owners of inexpensive motherboards will have no Phenom II upgrade opportunity, because most future models will have TDP 95W, and system integrators of compact computers are promised 65W and even 45W models (theoretically). Besides, there are a lot of motherboards supporting TDP 125W and higher. As they have been present in the market for a long time already, they come with affordable price tags and usually easy to find in stores. The most interesting chipsets for gamers are 790GX and 790FX, as they support CrossFire and can boast of rich peripheral functionality. We've selected contenders from what we have in our test lab.

By the way, most motherboards with these chipsets are equipped with excessive VRMs for Phenom II processors. They were designed for top Phenoms, and the first revision of 9950 had TDP of 140W. On the other hand, the official 125W TDP for top Phenom II processors looks more like playing safe (as this parameter for Core i7 equals 130W, so there were no reasons to reduce it; and cutting this parameter means stricter selection requirements, which raises manufacturing costs and reduces production volumes of already insufficient (at first stages) GPUs). In fact, Phenom II does not grow very hot, we already figured it out, when we tested this processor in nominal frequencies. What's left is to overclock it.

All motherboards with old BIOS versions booted up correctly with Phenom II (they detected its clock rate, multipliers, and voltage correctly). But then we flashed new BIOS, of course (in Windows) to run our tests with the latest version. It's good news, considering that stores often sell motherboards with old BIOS versions. In this case users won't have to choose a compatible processor to flash their mobos or to address their service providers.

Even moderate overclocking usually implies raising the core voltage. Specifications of the current stepping (C2) mention the working range of voltages from 0.825V to 1.5V. And AMD does not recommend voltages above 1.55V for overclocking with air cooling. However, even Phenom II X4 940 requires no more than 1.35V in the nominal mode, which leaves a considerable margin for safe voltage increase.

Maximum safe temperature of the processor package is 62°C. As far as a cooler is concerned, we installed Zalman CNPS9700 AM2. It's a relatively old cooler. We bought it several years ago, and even then it was not a new product. However, it's a popular, efficient model. Besides, we are not going to break records here. That is we did as most common users -- if you can install one of your old coolers, why not? And when you want acoustic comfort or higher cooling capacity (in summer), you may fork out for some trendy Thermalright or Xigmatek. If you choose new PC parts for overclocking, it certainly makes sense to spend some more time on choosing a better cooler.

What concerns a power supply unit, its choice is determined by your graphics card. As we are going to overclock a top model in the series, it's only natural to install the most power graphics card -- ATI Radeon HD4870 X2. So we had to use a 750W PSU (Seasonic M12D-750).

Overclocking

Even though Phenom II X4 940 has an unlocked multiplier, we initially overclocked this processor with a fixed multiplier by increasing the Base clock rate.


Board Core clock (multiplier), MHz CPU NB clock (multiplier), MHz Voltage, V Base clock rate, MHz
ASUS M3A79-T Deluxe 3825 (x15) 2295 (x9) 1.52 255
Foxconn A7DA-S 3810 (x15) 2286 (x9) 1.52 254
Foxconn A79A-S 3825 (x15) 2295 (x9) 1.52 255
Gigabyte MA790GP-DS4H 3840 (x15) 2304 (x9) 1.52 256
ASRock AOD790GX/128M 3855 (x15) 2313 (x9) 1.52 257

Even these results get it borne in that it's much easier to choose a motherboard for overclocked Phenom II than for Phenom. Yep, it sounds very strange, as we managed to overclock our sample to impressive 3800MHz, and it's not even the best result for Phenom II, as you may read in overclockers' forums. The first explanation that comes to our mind is significantly reduced power consumption. By the way, Phenom processors (B3 revision) have no real problems with their power consumption at nominal frequencies either. But when overclocked, a motherboard must really supply high currents (in tests and programs with high CPU load). And preserving stability in these conditions is precarious at best. To keep the system stable, VRM must be cooled well. Besides, design peculiarities also make themselves felt, hence different overclocking results of various motherboards.

Here is an illustrative example of moderate power consumption of overclocked Phenom II processors with an inexpensive ASRock motherboard. It has no heatsinks on MOSFETs, but it still became a formal leader of this test (in fact, the difference of 2-3MHz in Base clock rate can be written off to peculiarities of our samples). On the other hand, temperatures of VRM heatsinks on other motherboards did not exceed the environment temperature, while MOSFETs and chokes on the ASRock AOD790GX/128M were rather hot, so we cannot recommend installing it in a small PC enclosure. In other words, it's up to you to decide whether it's worth paying some more money for extra reliability or just install a fan on the rear panel (choose a proper case CPU fan that can blow at the VRM, etc). Creative activity, overclocking. What's more important, processors themselves have grown much friendlier to overclockers.

Reducing the CPU NB multiplier (in motherboards supporting this option) did not improve overclocking results, so we left this multiplier on the initial level (x9). By the way, the relatively low default multiplier plays into the hands of users that own motherboards without this option. On the other hand, increasing the CPU NB frequency is justified, because other than overclocking CPU cores, it affects the general performance level, especially in memory-heavy applications.

And now let's see what we've got with overclocking using multipliers.


Board Core clock (multiplier), MHz CPU NB clock (multiplier), MHz Voltage, V Base clock rate, MHz
ASUS M3A79-T Deluxe 3838 (x19) 2222 (x11) 1.52 202
Foxconn A7DA-S 3838 (x19) 1816 (x8) 1.52 202
Foxconn A79A-S 3857 (x19) 1824 (x8) 1.52 203
Gigabyte MA790GP-DS4H 3876 (x19) 2288 (x11) 1.52 204
ASRock AOD790GX/128M 3876 (x19) 2288 (x11) 1.52 204

Practically the same results. In other words, overclocking our processor (our sample) by increasing the Base clock rate is not much worse than "self-contained" overclocking with a CPU multiplier. However, overclocking within 3.6-3.9 GHz is typical of the first samples (given to testers, journalists, motherboard manufacturers, etc). Processors that go to stores may overclock even to 4.0-4.1 GHz without much trouble. It may be justified to overclock the cores of such processors with the multiplier. But even in this case, you'd better combine both approaches, if your motherboard does not allow to modify CPU NB multiplier, like both Foxconn models. You may want to do that to raise frequency of this part as well.

By the way, Advanced Clock Calibration, that affected Phenom overclocking so much, is now integrated into the processor. It will certainly please owners of early motherboards with the 790FX chipset and SB600 Southbridge, which did not support this technology. Enabling ACC on motherboards with this BIOS option does not affect overclocking results at all. It may even hang some motherboards, which BIOS is not optimized for Phenom II, so that you have to reset settings.

In other respects, we found no inadequate responses to the CPU upgrade. That was to be expected, as Phenom II demonstrates self-sufficiency even in power saving issues, which usually depend on a motherboard. We usually disable dynamic frequency control technologies (Cool'n'Quiet) in our performance tests, today is not an exception. After we increased frequency and voltage, idle CPU temperature remained on the same minimal level as before. That is idle units of this processor consume very little power even at high clock rates. To all appearances, that's the effect of AMD CoolCore technology: it dynamically disables idle units of a processor. We have no other explanations how this processor copes to cool down to the environment temperature, when it's idle. It's an autonomous technology that does not require drivers or BIOS options. Besides, the processor supports Cool'n'Quiet 3.0, which allows to reduce the idle temperature to 800MHz now. And the coming version of AMD OverDrive promises a combination of dynamic overclocking and reducing frequency depending on the load.




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Page 1: Intro, theory, overclocking

Page 2: More overclocking, conclusions



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