P8Z68-V Pro Overclocking

The Cougar Point/Sandy Bridge platform brings major changes to the overclocking process. Here are the bullet points:

• Overclocking by increasing the base clock is no longer an option.
• Overclocking by increasing the CPU's base multiplier is no longer an option.
• Only the P67 and Z68 chipsets support CPU overclocking at all.

Intel's new chipsets derive almost every clock on the motherboard from the base clock (BCLK) frequency. This makes board design simpler and more reliable, but it also means that raising the base clock raises other clocks on the system...like, say, the PCI-E slot clocks, the SATA clock, and so forth. What this means in practice is that you'll be lucky to raise the BCLK as much as 5MHz without crashing your system. An overclocking mechanism enthusiasts have used for more than a decade is consigned to the dust bin of history.

Intel compensates for this by giving all Sandy Bridge processors unlocked multipliers: K-series processors get "fully unlocked" multipliers with no limits, while non-K series processors are "limited unlocked" CPUs that can only have their multipliers increased by a maximum of 4. All Sandy Bridge processors have fully unlocked video cores, RAM multipliers, and power settings, so you can tweak your RAM and on-board video with any motherboard.

You overclock a Sandy Bridge CPU by increasing the Turbo multiplier: that is, the one the CPU uses to automatically increase the clocks speed of its cores under load. If you raise the multiplier on a Core i7 980X Extreme chip, you're increasing its speed in all situations: idle and load. Raising the multiplier on a Sandy Bridge processor only raises the speed it will ramp up to under load; its idle speed remains the same. While this might seem limiting, in practice it works really well, since Turbo Boost is very, very good at deciding when to ramp up the clock speeds, and you benefit from dramatically reduced power consumption in low-load situations. Initially I didn't like this new overclocking mechanism but have come around after a few months' experience with it, and the older mechanisms now seem primitive. Since most of the overclocking mechanisms are built into the chip, the motherboard itself becomes less of a factor in overclocking than it was in the "raise the BCLK" days. Benchmark Reviews has published an in-depth article on Sandy Bridge overclocking.

ASUS provides a number of automatic overclocking mechanisms in the P8Z68-V Pro motherboard: you can start an auto overclock session directly from the UEFI BIOS, or take more control with ASUS' Turbo V Evo software. I'd recommend the latter for overclocking beginners: it generally achieves very stable results with good performance increases with almost no effort on the part of the user. However, so far, no automatic overclock mechanism can achieve the results of hand-tweaking. Still, the Turbo V Evo utility is very useful for experimenting with overclocking since it can make all the changes "live" while in Windows, without having to reboot each time as you do with settings changes in the BIOS.

In the "A.I. Tweaker" section of the BIOS, I achieved my best results with a BCLK of 103MHz and an "all cores" multiplier of 48, resulting in a final Turbo Boost overclock of 4.94GHz.

Try as I might, the magical 5GHz mark remained just out of reach. Since you can specify different overclocks on a "number of cores in use" basis, given more time I probably could have reached 5GHz in a single-core situation, but under Windows 7 there's never only going to be a single core in use, so the time spent at 5GHz would have been minimal. And given the amazing performance at 4.94GHz with all cores, I'm not too disappointed. This is 200MHz higher than I was able to get with my previous 2600K overclocking experiments with ASUS' P8P67 EVO motherboard.

You do have to be careful about one thing: with older processors, you knew your overclock failed when your system crashed. Sandy Bridge CPUs, on the other hand, are very clever about automatically reducing their clock speed when the CPU core temperature gets too high. You might think that overclock is working perfectly, but behind the scenes your processor is clocking itself down when things get too hot. Keeping a utility like CPU-Z open during your stress tests will let you see the core speed "live" so you'll know if this happens.

This overclock represents a 29% overclock from the standard 3.8Ghz Turbo Boost frequency, and applies to all four cores under load rather than the single core the stock 3.8Ghz applies to. This performance differential was reflected in the benchmarks. This is the highest "on air cooling" frequency I've seen with an Intel quad-core processor.

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