Overclocking Results
Overclocking Results
First and foremost, if you are completely new to Phenom II overclocking we highly recommend that you check out our article on the subject, aptly titled
"Hardware Canucks: Benchmarkers Guide to the Phenom II". Although it is limited to the AM2+ versions, the fundamentals remain the same as with the new Phenom II AM3 processors.
In our tests, we will be using a Phenom II X3 720 Black Edition processor, codename 'Heka', which is obviously a triple-core model. It features a 2.8Ghz clock speed, 1.5MB of L2 cache, 6MB of L3 cache, and most important for our purposes, fully unlocked CPU multipliers. As a result, we will be able to determine what kind CPU bus speeds this motherboard is capable of, with both the IGP enabled and disabled. We'll also be seeing how well our processor scales on this model, although we don't really a point of reference to compare it to yet as this is our first AM3 motherboard. Lastly, and the whole point of the AM3 platform, is the DDR3 memory, and we'll see what kind of memory speeds we can achieve using two modules from our recently reviewed
OCZ 6GB PC3-12800 Platinum memory kit. Across four results, we have disabled Cool'n'Quiet and C1E in the BIOS, and we kept the CPU/NB frequency and HT Link speed as close as possible to their default 2000Mhz mark.
So without further ado, let's move onto the results:
Highest Stable CPU Bus Overclock
Much like the Intel Core i7's base clock (bclock) frequency, Phenom II's have a CPU bus frequency that is generated and thus limited by the motherboard. Although this frequency is more or less relevant on an unlocked CPU multiplier chip like the one we are using, those who purchase the X3 710 and X4 810 will need to increase this bus frequency in order to overclock their processors. As you can see above, our unit proved to be a very capable overclocker. From the stock 200Mhz, we were able to achieve a heady 285Mhz. To put that into perspective, this would permit you to overclock the 710 or 810 (both have a 13X multiplier) up to a solid 3700Mhz. This result was dead simple to achieve as well. No special tricks or tweaks, we just left all the voltage options on AUTO, manually selected an appropriate memory frequency, and started increasing bus frequency until we found the high mark. The epitome of simplicity.
Having said that, we did notice an "FSB Hole" in the 240Mhz range, in which the system was inexplicably unstable. Contrary to common logic, the solution was simply to overclock the system higher and stability was no longer an issue once we reached the 250 mark. From what we've been reading on various message boards this "FSB Hole", if present at all, can appear anywhere in the CPU bus frequency range so it can be somewhat troubling to diagnose properly. Therefore, keep this in mind if you do own and overclock with this motherboard. This issue is present with BIOS version 0801, and it is quite possible that ASUS will rectify this issue in a future BIOS update.
Highest Stable CPU Bus Overclock - IGP Enabled
Since Radeon HD 3300 integrated graphics processor is an integral part of the 790GX northbridge, we were very interested in determining whether having it enabled would have any impact on the overclocking of the bus frequency. As you can see, it did have an impact, but a relatively small one. In our eyes, a 10Mhz loss is quite acceptable in exchange for the free functionality of the IGP. It is good to see that those who are more interested in pure CPU power than fancy graphics will not be held back when overclocking with the IGP in use.
Highest Stable CPU Overclock
By now most of you are aware of the Phenom II's vastly superior overclocking capabilities when compared to the original Phenom processors, and clearly the switch to DDR3 has not had a negative impact. While our CPU overclock is not as remarkable as all the 4Ghz results we are seeing everywhere, it remains a solid 32% overclock. As we mentioned previously, we have no point of reference with this processor. Therefore, we cannot be 100% sure that it would not achieve a superior result on another motherboard, however we have no reason to suspect that the M4A78T-E was holding back our progress in any way, shape, or form.
Highest Stable Memory Overclock
Finally...DDR3 on an AMD platform, terrific right? Regrettably, at least at this point in time, it does not appear that the new AM3 integrated memory controller has much headroom when it comes to memory overclocking. We tried everything; every voltage option, timings, skews, drive strengths, tweaks, and tricks but to no avail. No matter what 4GB DDR3 memory kit we used, there simply no way ensure stability above 1660Mhz. Other Phenom II AM3's might be slightly better, but there is a reason why memory manufacturers haven't really jumped on the AM3 bandwagon. To ease the strain on the IMC, we whipped out of our best DDR3-2000+ capable 2GB kit, and although we were able to achieve up to 1760Mhz with stability, anything higher would fail our stress tests. In order to achieve these results, we used up to 1.4215V for the CPU/NB, any higher did not increase stable memory overclocking headroom. As important as the CPU/NB was the NB voltage, which we had to increase to 1.40V in order to reliably load Windows.
Although we kept the CPU/NB (ie: integrated memory controller) frequency as close to the stock 2000Mhz as possible during our tests, this is the frequency that you want to increase in order to achieve the
best possible bandwidth numbers. In doing so however, we encountered a slight BIOS issue. Anytime we selected a CPU/NB frequency above 2900Mhz it would simply revert back to the stock 2000Mhz. We're hoping this gets fixed in a future BIOS update since our processor definitely seemed to have some additional headroom.
