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Overclocking The first analysis of the Phenom 940 will be its overclockability. Informed readers will know that the original Phenom had about the same clock efficiency as Kentsfield, but was hampered by its lackluster overclocking overhead. If Phenom II can siginificantly improve its overclockability, then it has a chance at competing with Yorkfield. So does it? First off, let's take a look at our system specifications:
According to AMD, all AM2+ motherboards should be Phenom II compatible with a BIOS flash. Currently AMD is recommending three motherboards: the above Asus board, the MSI DKA790GX Platinum, and the Gigabyte MA790GP DS4H. Now overclocking an unlocked Black Edition is quite a bit different than overclocking an Intel CPU. On an Intel setup, because all except the most expensive CPUs have upwardly locked multipliers, all OCing is done through FSB. Because of this, there are many variables that must be taken into account, including RAM speeds, timings, and GTLs for the CPU and North Bridge. Overclocking an unlocked CPU is a completely different (and easier) beast. In the past unlocked CPUs were reserved for the top end, but some time ago AMD released "Black Edition" CPUs that brought unlocked overclocking to the masses. What makes an unlocked CPU so great? Overclocking via the multiplier is much easier to do; since the AM2+ already has plenty of memory bandwidth to spare, all you need from a motherboard is sufficient power modulation and voltage. This makes overclocking easier on cheaper motherboards, making the whole platform cheaper. This is what makes the Phenom II 940 Black Edition so tempting. Given the nature of the unlocked CPU, and the 200MHz HTT clock, we can then easily overclock in 100MHz increments; any finer tuning must be done by adjusting the HTT clock.
Overclocking the X4 940 showed some very interesting results. Each step went through a 4 hour validation with Prime95 LargeFFTs to ensure stability. Instead of a steep voltage wall, overclocking speed was nearly linear with voltage increases. What I also found is that the X4 940 is very sensitive to temperature. Initially overclocking on the OCZ Vendetta II, I was able to reach 3.5GHz at 1.5V. While load temps were still under 55C, I was convinced I could push further. At that point, I put on the Swiftech H2O-220 Compact to see what else I could squeeze out of it. I topped out at 3.7GHz at 1.575V, with a mere 35C load temp. After that, no amount of voltage afforded any further increases, even up to 1.65V. All in all, I have to say the headroom has been vastly improved over Phenom I, and the temperatures are equally impressive. This also affords more options for the cost-conscious overclocker.
So that tells us only part of the story. Overclocking is one end of it, the other end is the actual overclocked performance. So we are going to look at a bunch of different tests at different speeds to see how this chip performs.
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