Overclocking analysis: hands on with Sandy Bridge-E

When Intel released its P67 chipset enthusiasts were excited that they could break the 5GHz barrier using low-end air cooling but somewhat disappointed that Sandy Bridge was unable to reach the lofty mid-6GHz frequencies of the earlier X58 and Gulftown. Unfortunately for those holding their breath it’s high unlikely Sandy Bridge-E will ever reach the same frequencies as Gulftown did but it still has a lot to offer.

There are a plethora of changes in Sandy Bridge-E that will have a massive impact on overclocking.

First and foremost are the additional cores which bring the kind of increased heat load that we traditionally associate with decreased overclocking capacity. The high-end Sandy Bridge-E 3960X CPU also has a 15MB cache almost double the 8MB on board the last generation 2600K CPU and this could also limit the CPU frequency. Previously on X58 motherboards we had the option to lower the cache frequency by adjusting the uncore multiplier but since the release of P67 and continuing throughout X79 the uncore frequency is synchronously locked to the CPU. This means a CPU’s maximum frequency is potentially limited by the maximum frequency of the cache.

Adjusting the base clock on X79 takes a while to get used to. Formerly on P67/Z68 we would slowly raise the base clock while adjusting the VTT voltage until a maximum frequency was achieved. On the X79 platform there is both the base clock and base clock multiplier that require tweaking to reach the maximum frequency. Changing the base clock multiplier from 100MHz to 125MHz subsequently adjusts your default base clock to 125MHz and gives you the option to further adjust your base clock both up and down from this frequency.

For example if your target base clock frequency is 120MHz then you may need to change the base clock multiplier to 125MHz and then lower the base clock to 120MHz. If you were to leave your base clock multiplier at 100MHz and change your base clock directly to 120MHz your overclock would likely fail as the frequency jump is too large. This is going to complicate the overclocking process and is a throwback to the straps that Intel used on its X48 platform.

Of course anyone purchasing a 3960X or 3930K won’t need to worry about adjusting the base clock as the multipliers are unlocked. Overclocking the Sandy Bridge-E chips by adjusting the multiplier is identical to P67/Z68 just set and forget. The voltages weren’t very far off P67/Z68 either sitting in the 1.45-1.525 range.

We tested a number of chips and found they were all able to benchmark between 5100 and 5300MHz on the Intel water cooler. While the Asetek designed water cooler does a great job of keeping the CPU temperature under control it’s an optional extra as Intel has decided not to bundle any coolers with its latest chips.

Possibly the most anticipated aspect of X79 is the introduction of quad-channel memory and the increases in memory frequencies on offer. Most of the top memory manufactures are offering 16GB kits with frequencies of around 2400MHz. Unfortunately not all CPUs are blessed with the ability to reach 2400MHz. It really is a lucky dip. This might leave some users in an awkward situation; not realising their memory frequency issue is a CPU limitation and trying to get a warranty replacement on their memory kits. However those lucky enough to get a CPU capable of passing 2400MHz have access to monstrous bandwidth that is up to 25% greater than P67/Z68.

Overall Sandy Bridge-E is big step forward in memory bandwidth and multi-threaded applications and will finally make both Gulftown and the X58 platform obsolete.