iXBT Labs - Computer Hardware in Detail






AMD Phenom II X3 720 and X4 810 Processors

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Processors are usually overclocked for two reasons: sportive and practical. The overclocking sport suggests reaching an ultimate performance level, not available for production-line processors. For this purpose overclockers usually buy top processors, and then install expensive liquid cooling systems or even freezers to reach fantastic operating frequencies, which won't become nominal for the nearest couple of years in the very least. By the way, Phenom II is a very interesting product from this point of view, as it does not contain the so-called cold bug, that is, it can work even in low-temperature conditions, for example, cooled by liquid nitrogen or helium. In particular, a Finnish team has recently broken the overclocking record by forcing Phenom II X4 940 to run at 6.5GHz -- you can watch the video.

Practical overclocking does not imply breaking records, it's sole purpose is just to get higher performance for less money. In other words, high frequencies are not an end in themselves, what matters is how much you pay (prices for a motherboard, coolers, PSU) to ensure stability of the overclocked system. In this case users choose promising inexpensive processors with high overclocking potential with air cooling (rarely water cooling). Note that cheaper Phenom II processors match this description, because, for one, they demonstrate good test results even at their nominal frequencies, and for two, they have an integrated DDR2/DDR3 memory controller and monolithic core architecture, hence good prospects for future multithreaded applications, and for three, they are manufactured by the most advanced process technology: 45nm SOI, which should contribute to the reduction of heat release even in an overclocked mode. However, overclocking non-top models (intended for enthusiasts and having special options to facilitate overclocking) requires following certain rules. There are certain tricks of the trade, which we're going to cover in this article.

Brief theory

Our Phenom II models can be installed on motherboards with Socket AM2+ as well as AM3. But we shall deal with the first option for now, as the most popular solution these days. We also have motherboards with DDR3 support in our lab, so the next question in our agenda is to compare system performance with different memory types. However, motherboards with DDR2 memory will apparently be the most popular platform at the first stage, especially for cheaper processors in this series. Some users will upgrade a processor and keep the old motherboard. The others, assembling a new computer, may compare prices for DDR2/DDR3 memory and choose this option as well, considering the wide choice of motherboards for Socket AM2+.

These processors have 95-W TDP, so the absolute majority of motherboards will bee able to work with them in nominal mode. However, you'd better choose a motherboard with a larger safety margin for successful overclocking. Fortunately, there are plenty of Socket AM2+ motherboards that support TDP=125W. This value is typical of Mid-End Phenoms, so manufacturers tried to install powerful power supply circuits even on inexpensive motherboards. This feature will come in handy now, it allows to reach high overclocking results without excessive investments into the platform. Practice confirms these results. We already figured out in our overclocking tests of Phenom II X4 940 on different motherboards that overclocking results practically do not depend on circuit design nuances of a motherboard. It's logical to assume that proper BIOS options will be crucial for Low-End models, which power requirements are even lower, and hardware characteristics (VRM parameters and so forth) will take a backseat. It goes without saying that some nuances will arise anyway, and we'll still pay attention to overclocking potential in our motherboard reviews. But if a motherboard copes well with Phenom overclocking, it will certainly do fine with Phenom II. So this time we perform all overclocking experiments on one motherboard: Gigabyte MA790GP-DS4H (BIOS F3).

Theoretical overclocking limits of Low-End models with increased voltage are wider than of High-End processors, because their nominal voltage is usually lower, while the recommended maximum is the same (1.55V). But in practice, raising voltage above a certain level often does not expand the overclocking potential, so an optimal value must be adjusted experimentally in each case. Maximum permissible temperature inside a PC enclosure is 71-73°C. However, most users used to maintain even CPU temperature at a lower level, and in such strenuous conditions PC components have to work only if integrated into some industrial plant equipment. However, stable temperature levels for an overclocked processor are always lower, hence the fashion for excessive cooling systems. Other things being equal, a processor that endures high temperatures at its nominal frequency has lower requirements to cooling when overclocked.

We've taken the same old Zalman CNPS9700 AM2, which coped with cooling the 940 processor overclocked to 3.8GHz. It should apparently cover the needs of our contenders with a margin. The same cooler was installed on the Intel Core 2 Quad Q8200 (using the retention module from the NT model), which took part in our tests for comparison (on an MSI P45 Neo3 V2 motherboard).

The graphics card was also the same (ATI Radeon HD4870 X2). But we didn't overclock it, so it was working at its nominal frequencies. Besides, we updated the video driver to Catalyst 9.2, as driver optimizations for new processors often yield good results (that's why test results in this case cannot be compared directly with our previous test results). A 750-W Seasonic M12D-750 was installed as a power supply unit. In fact, such high power capacity is not necessary. Even a 550-W AcBel ATX-550CA-AB8FB copes with this load.


To all appearances, our sample of Phenom II X3 720 was made a triple-core processor for natural reasons, that is, because of a defect in its fourth core. So when we tried to unlock it, our computer would just freeze so that we had to clear CMOS with a jumper. Judging by some forum posts, activating Advanced Clock Calibration in BIOS unexpectedly unlocks the fourth core in a triple-core processor (choose Auto). That's a generous bonus. To all appearances, it really exists, but it may be a total surprise to the manufacturer. In this case, if you want to get a potentially unlockable processor, you should hurry up, as this feature is currently reported available only in the first batches.

However, this procedure is not interesting from the point of view of overclocking tests. Such quad-core processors will most likely overclock worse (if at all). So it will hardly reach the same performance level as true quad-core processors (especially if we take into account the overclocking potential of Series 900). And we were interested how much we could overclock a triple-core model, so we took advantage of the unlocked multiplier in this processor and raised frequencies of the cores and CPU NB. Here is what we got.

CPU Core clock (multiplier), MHz CPU NB clock (multiplier), MHz Voltage, V Base frequency, MHz Memory clock (multiplier), MHz
Phenom II X3 720 (2.8 GHz) 3755 (x18.5) 2639 (x13) 1.50 203 DDR2-
1079 (x2.66)

Phenom II is still a joy. We'd like to evaluate the effect of raising CPU NB frequencies in our tests, which made no sense for the first Phenom processors (we could raise it only as far as 2200MHz, and we used to reduce the multiplier, when we had to overclock processors by raising the base frequency). Frankly speaking, in our tests of Phenom II X4 940 we didn't determine the maximum level of this frequency, sticking to 2200MHz. The memory multiplier was set to maximum (DDR2-1066) to obtain the frequency specified in the table (taking into account a small raise in bus frequency). By the way, the processor started up well, allowed to load Windows and even run some tests at up to 3.9GHz (cores), but we stick to the rule to publish values proved by a half-hour stability test from AMD OverDrive.

On one hand, Phenom II X4 810 promises to demonstrate a higher overclocking potential at lower voltage, generally typical of processors with smaller cache memory. On the other hand, overclocking processors only with the base frequency poses some problems. Fortunately, in case of the AMD platform, they can be solved by reducing HT bus and memory frequencies proportionally -- it can be done independently of the CPU clock rate. As overclocking HT bus has no effect on performance, we've always chosen the multiplier of this bus to get 2-2.2GHz -- this mode is guaranteed to work on all motherboards. What concerns the memory frequency, it makes sense to adjust it to get DDR2-1066 frequencies. Fortunately, our memory is designed to work at this frequency. But it turned out, this approach allows to squeeze only 3.5GHz from our processor. However, having reduced memory frequency to DDR2-800, we managed to get 3.8GHz. And the absolutely stable mode became possible after we rolled back only by 30MHz (at the low voltage).

CPU Core clock (multiplier), MHz CPU NB clock (multiplier), MHz Voltage, V Base frequency, MHz Memory clock (multiplier), MHz
Phenom II X4 810 (2.6 GHz) 3770 (x13) 2613 (x9) 1.47 290 DDR2-
772 (x1.33)

Interestingly, necessity to set this memory multiplier does not depend on the real CPU NB frequency, which increase could have been caused by the non-standard memory load. That is, even having set this frequency to the standard value, you can overclock the cores only after reducing the memory frequency. What's even more interesting, there is no such effect on the platform with DDR3. On the contrary, overclocking memory is possible and limited only by memory properties. This way our processor reconciled itself with the base frequency of 300MHz, and our memory coped with the multiplier that made it work as DDR3-1600! Thus, this processor supports a special type of overclocking with a continuation. For example, you can install this processor into your old system and don't worry about "lost opportunities" with the standard DDR2-800 memory, as DDR2 memory won't operate at a higher frequency anyway (to be more exact, only at the nominal frequencies or with weak core overclocking). And later on, when DDR3 memory and corresponding motherboards obtain attractive prices, you will carry on with your experiments.

By the way, if you don't have a powerful cooler, the following strategy makes the most sense: increase voltage only to 1.45-1.48V and overclock the system gradually, step by step. In this case you may even get better results than by setting the maximum voltage at once (1.55V for air cooling). A stable maximum value may be much lower. As a rule, CPU NB voltage should be smaller than core voltage, if your motherboard can do it.

Let's sum up motherboard requirements for hardcore overclocking of Phenom II X4 810 on the Socket AM2+ platform:

  • Adjustable CPU NB multiplier (as a rule, you will have to reduce it by one step)
  • Memory multiplier x1.33, which corresponds to the nominal DDR2-533 frequency
  • Option to increase the base frequency to 290-300MHz.

Another important note: make sure Cool'n'Quiet is disabled in BIOS when it's set to Auto, some motherboards still try to reduce voltage, which leads to instability). If you want to overclock the system only for heavy applications (for example, games), you can use AMD OverDrive and create a profile in Fusion for gaming to activate overclocking when necessary.

We should add a few words about overclocking Core 2 Quad Q8200, which gives us results for comparison. The overclocking community have already examined this processor inside out, and we have nothing to add. In brief, because of the relatively low multiplier (x7), overclocking in most cases is limited by stability of FSB operation at high frequencies. As "halves" of this processor have to exchange data via this bus (Core 2 Quad consists of two dual-core dice in a single package, which exchange data via the chipset), the load on this bus and chipset is very high. So you will be lucky to overclock this processor to 3.4GHz. In our case, the stable values were FSB=473MHz and core clock a tad higher than 3.3GHz (voltage raised to 1.40V).

It's time to see how much our efforts will bring in terms of fps gains in the most interesting applications -- modern games.

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Page 1: Intro, theory, overclocking

Page 2: Effect on games, conclusions

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