CPU Tweaks

There's more to prepping a rig for a new CPU than just setting the FSB

Power Struggle

If you’re used to poking around the BIOS, you don’t need to be told that the CPU’s overall clock speed is determined by multiplying the CPU’s clock multiplier by the front-side bus. In other words, the overall clock speed of a CPU with an 8x multiplier and a front-side bus of 400 is 3200MHz.

What you might not know is the purpose of some of the more obscure CPU-related BIOS settings. Both C1E and EIST relate to power-saving techniques employed by Intel CPUs. EIST, or Enhanced Intel SpeedStep Technology, is an offshoot of the notebook SpeedStep feature that lowers the CPU speed when it’s not under heavy use. C1E is an enhanced halt state that cuts the clock multiplier in the CPU to a preset value when the OS tells the chip that it has no work for it. Each has pros and cons. EIST is known for greater granularity, ramping up and down depending on load, but it does require driver support in the OS to manage it. Critics say EIST can actually reduce performance since it’s designed to operate the CPU at lower speeds whenever it’s not running at 100 percent capacity. The C1E state is issued by the OS when it’s idle, so C1E doesn’t require quite as much management. But some overclockers prefer to disable C1E since it can interfere with overclocks. We’ve seen older boards feature settings for both, but in our experience, newer chipsets from Intel contain settings only for C1E. Flipping off the features will force the CPU to always run at its maximum clock speed. Phenoms have similar features with Cool’n’Quiet (akin to EIST) and now C1E support. While you’re not supposed to, we’ve run with both settings on without issues, but your mileage may vary.

New CPUs include thermal sensors that slow down the CPU when it overheats. If you’d rather have your machine bluescreen instead of slow down (perhaps for stress testing), you can switch CPU Thermal Control in the BIOS to Off. NForce chipsets actually let you select between lowering the CPU clock speed, or cutting the multiplier and voltage, or both. Since we’d rather lose performance than outright crash, we normally set the BIOS so the clock speeds drop.

Virtually Useless

Some overclockers prefer to turn off virtualization support—not a bad idea if you don’t run any vitualization software.

One CPU setting that can probably be turned off by most folks is VT, aka Vanderpool or Virtualization support. The setting enables virtualization hardware support in the CPU for, well, virtualization. It basically turns on the hardware “acceleration” capabilities when using such applications as VMWare or Virtual PC. If you don’t run virtualization, it’s completely unnecessary. If you do, well, don’t expect miracles since hardware acceleration of virtualization is still in its early phases.

Protective Measures

This BIOS has Execute Disable technology as well as Enhanced Intel SpeedStep and C1E enabled.

The Execute Disable option is a switch in the BIOS that prevents many buffer overflow attacks, whereby malicious programs are able to circumvent security by putting viral code in RAM and executing it by intentionally overflowing the buffer. AMD created the feature and calls it NX. Intel’s clone of it is called XD. Both do the same thing. There’s some disagreement whether it hurts or helps though. Some people have reported problems with overclocking when Execute Disable is on, while others claim it’s not an issue.

Our take is to leave it on unless you’re specifically having problems with it—on the other hand, we’re skeptical whether the feature makes a lick of difference. If it did, wouldn’t it make Windows XP SP2 machines totally secure? Right.

To verify that hardware data execution protection is enabled, go into Windows, hit Start, then Run, and type CMD. Enter the command wmic OS Get DataExecutionPrevention_Available. The response should be “true.” Or simply download Gibson Research’s SecurAble, which will scan your machine to verify protection.

Don't Do It: BIOS Tweaks to Avoid

Just because it’s in the BIOS doesn’t mean you should touch it. Such is the case with PCI Express overclocking. Notoriously finicky and known to cause crashing, overclocking the PCI Express bus in the hopes of getting more GPU performance rarely ends well. In many cases, overclocking the PCI-E bus by even 1MHz beyond its stock 100MHz can cause instability.

Want a really good example? Nvidia made much hay of the Linkboost feature in its 590 SLI and 680i SLI chipsets. Linkboost would automatically overclock the PCI Express slot by up to 25 percent when paired with GeForce cards.

We never could understand the need for Linkboost, as PCI Express bandwidth was so great to begin with. Nvidia must agree now too. The company has removed the feature completely from the newer BIOSes for those motherboards.
You might also be tempted to disable USB legacy support since the feature lets USB keyboards and mice work in DOS mode, and, well, who the hell runs DOS anymore? You do—if you boot into safe mode. With USB legacy support disabled in safe mode, your USB input devices would be rendered useless.

Next: Voltage Tweaks