P7H55D-M Overclocking Features

With Intel moving more features from the chipset to the processor, the motherboard's role in overclocking arguably changes from overclocking its own components to supporting the overclocking of the processor and memory. And while it might seem that an H55 motherboard's role is best realized in a small, quiet home theater PC (and indeed the ASUS P7H55D-M EVO would serve well in this situation), ASUS has nonetheless stuffed this motherboard with all the hardware and software features required to support extreme overclocking. After all, it's hard to argue with a stable 4.64GHz Core i5-661!

Hardware Overclocking Support

On the hardware side, ASUS provides a robust "8+3 phase" power supply with ferrite chokes and solid capacitors to ensure the processor and components have clean, stable power; an 8-pin EPS-12V connector ensures adequate power is available. The system provides the fast transient response needed: when going from idle to full load under a heavy overclock, the processor's power consumption can more than double in less than a millesecond. If your motherboard's power supply isn't up to the task, a sudden voltage drop might occur that could crash the system. The ASUS P7H55D-M EVO was stable under all testing.

ASUS also provides a number of features that make overclocking on this motherboard simple and convenient. If you crank your memory frequency too high and render your system unbootable, pressing and holding the "MemOK!" button on the motherboard for a few seconds will reset the memory speed to a known good configuration without resetting your other BIOS changes. I did miss the power and reset switches and "clear CMOS" button found on ASUS' other enthusiast-level motherboards, though.

Software Overclocking Support

This is where the P7H55D-M EVO really shines. Not only does ASUS include the very comprehensive "AI Tweaker" section in their BIOS, but they also include a number of Windows-hosted overclocking utilities. First, I looked at the BIOS, since this is where I'm used to doing overclocking. The main AI Tweaker screen offers several "quick" overclocking options from the "Ai Overclock Tuner" item: Auto, which is the default setting, runs everything at stock speeds, while XMP will adjust the base clock frequency to run your memory at its XMP-defined settings (if you have XMP memory). If your memory's overclockable, but doesn't have an XMP profile, you can use the D.O.C.P. (DRAM OverClocking Profile): set your memory's rated speed, and the Ai tuner will adjust your BCLK so that your memory runs at that speed. Manual allows complete control of all parameters. I used Manual for my tests.

A somewhat mysterious option is the BCLK/iGPU Frequency Sync Mode item; according to the explanation at the right of the screen, if it's disabled, iGPU frequency will be adjusted according to the base clock, while iGPU voltage will be adjusted according to the base clock if it's enabled. The default Auto option's effects aren't described, and ASUS' manual doesn't mention the option at all. I left the setting at Auto and adjusted the iGPU frequency and voltage manually for my tests.

Additional sections of the Ai Tweaker page offer very detailed control over memory timings and voltage. ASUS suggests setting the timing mode to "1N" for best performance...if your memory will handle it.

The iGPU settings aren't in the Ai Tweaker section; they're in the Uncore selection of the Advanced section. But as our tests show, there's really no reason to overclock the iGPU, although you'll need to underclock it if you're overclocking the processor.

The Ai Tweaker settings are impressively comprehensive, but I found the Windows-hosted software to be more interesting. Some of the software, such as the EPU-6 Engine and GPU Boost, are driver-level items that enabled functions but have no user interface of their own. But the Turbo V and Turbo Key utilities are what made overclocking this board a pleasure, with a little support from Fan XPert.

Versions of the Turbo V utility are becoming common across ASUS' line; basically, it lets you adjust the voltage and frequency to both the processor and the iGPU (you must have installed the GPU Boost driver for the latter feature to work) in real time, right inside windows:

Simple drag the sliders to the settings you want and click "Apply" to instantly adjust your board. You can save any group of settings in a "profile" and recall it from the menu. The advantage of homing in on your best overclock this way is that the settings are not saved in the BIOS: so if you crash or freeze— and you will, of course— your system will reboot with the stock timings and you can try again. Once you find the settings that work best for you, you can either manually enter them into the BIOS, or simply pick them off the menu in the Turbo V utility.

The relationship between the CPU base clock (BCLK) frequency and the iGPU frequency is a matter of some mystery: neither Intel nor ASUS provide any documentation on the relationship, but tests show there definitely is one, probably based on some multiplier. I had to reduce the stock 900MHz frequency of the iGPU to 700MHz in order to achieve stable operation at a BCLK of 185MHz, but the true frequency the iGPU was running at is unknown.

You can configure the "GPU Boost" feature to automatically overclock the iGPU when its load increases, but frankly this strikes me as almost useless: as seen in the performance tests above, the iGPU, even overclocked, is useless for gaming, and it performs to spec just fine at the stock speeds.

Turbo Keyis a small utility that works with the profiles you created in Turbo V:

It's very simple, yet very useful: when it's enabled, your computer's power button acts as a toggle between stock clock speeds and voltages, and whatever profile you've selected. This is perfect for a system like this, as you can benefit from the low power consumption of a Core i3 or i5 system, and instantly crank it up for gaming or other CPU-intensive activities. Remember the doubled power consumption I noted earlier? Now, this consideration almost vanishes, since you need only tap the power button to switch back to a low-power mode when you're done with whatever you were doing that needed the extra performance.

ASUS' Fan XPert allows you to set performance profiles for the CPU fan and chassis fan. You can select from pre-defined profiles such as "Silent" (slow fans), "Turbo" (fast fans), and "Intelligent" (temperature-based fan speeds), or create your own profiles for the either fan.

Overclocking Results

Using an Intel Core i5-661 processor, I managed to get a stable overclock at a BCLK frequency of 185MHz at 1.4 volts, resulting in a core frequency of 4.64GHz, with the GPU frequency set to 700mHz (although what frequency it was really running at, probably more than 700mHz, is unknown). The system would boot and run Windows at a base clock of 190mHz (4.75gHz) but would fail under stress testing. I could use the Turbo Key utility to switch between normal and overclocked profiles, even in the middle of a performance test, with no problems.

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