Voltage Tweaks

They say no pain, no gain. But it’s really no voltage tweaks, no high overclocks. While the risks are great, overvolting can pay some great rewards

A reader recently asked us whether heat or voltage was more dangerous to a CPU. Hands down, we’d say voltage is far more dangerous. All modern CPUs have a built-in limiter that throttles the CPU if it overheats. The same is not true when a chip receives more voltage than it was designed for. Clearly, this is the most dangerous part of mucking around in the BIOS. If you’re faint of heart and don’t like to break things, don’t mess with voltage tweaks. However, if you’re looking for that extra bit of performance, voltage tweaks are often the only way to get there.

Modern motherboards will let you turn all kinds of voltage knobs, but the basics are CPU core voltage, RAM, and chipset.

If you read our sections on memory timing and speed, there’s one very important fact you need to know: You’ll likely need to overvolt your high-performance RAM modules to hit their rated speeds. DDR400 officially tops out at 400MHz, and DDR2 tops out at 800MHz. Anything higher is technically beyond JEDEC specification and invariably requires overvoltage to hit. In fact, you’ll notice that much of the high-performance RAM today will include recommended voltage settings needed to hit the clock speed and timings it boasts.

Most high-performance RAM requires running out-of-spec voltage on the modules.

DDR’s spec’d voltage is 2.5 volts. DDR2’s is 1.8 volts,  and DDR3’s is 1.5 volts. To give you an idea of how much additional voltage you need to overclock RAM, consider this: To get a typical DDR2 DIMM to go from DDR2/800 to DDR2/1066, you have to push the voltage to 2.20 volts. To get a DDR3 module to reach all the way to DDR3/1800, you have to push two volts. If you ask us, that’s an awful lot of voltage, and your modules probably aren’t going to last several years at those levels. On the other hand, what enthusiast is going to run the same RAM for five years anyway?

Which bring us to the age-old question: “How much voltage do I run?” For RAM, we recommend that you follow the manufacturer’s settings, as that will be the best indicator of the module’s overclocked speed and voltage needs. For CPUs, it’s chip dependent. One way to judge how far you can push your chip’s voltage is to cruise forums at MaximumPC.com, Anandtech.com, HardOCP.com, or any of the numerous forum boards out there to see what people are running for your particular CPU. One new development we like is the danger gradations in some vendor’s newer BIOSes.

Older BIOSes simply let you select how much additional voltage to add to the CPU without any regard for the risk. Some newer BIOSes will actually indicate by color how hazardous your voltage increase is. Gray is mostly safe while red indicates nuke potential. Since we figure the board engineers are basing their threat levels on lookup tables based on the CPUs themselves, we feel pretty confident cranking up CPU voltage to just below the red zone.

How you change voltage settings will vary greatly from board to board.

BIOSes today also let you increase voltage to the north bridge and south bridge separately, and in most nForce boards, even the HyperTransport link between the north bridge and south bridge can be overvolted. Do you really need to do this? We’ve found that, yes, you do need to goose the north bridge voltage on occasion to get stable upgrades, but like CPU and RAM overvolting, it’s quite risky and can damage the board when done without caution. Take our previous advice: See what works for others before jumping in with both feet.

Odds and Ends

Before you POST your new system to install the OS, you should disable unneeded ports and make your decision to run either AHCI or IDE

When we build a new system, one of the first things we do is flip through the BIOS, turning off things we know we won’t ever use, such as the serial port and parallel port. If your system doesn’t include a floppy drive (some still do), we also flip off the floppy controller in the BIOS. Turning these features off saves some system resources, but it mostly just makes us feel good.

Turning on AHCI mode will require installing drivers via F6 with Windows XP.

If you dig into your BIOS you’ll also see a setting that lets you configure your SATA ports as IDE, RAID, or AHCI. Default should be IDE and most people understand that setting RAID turns on the RAID features of the chipset, but just what is AHCI? It’s the Intel specification dubbed Advanced Host Controller Interface that enables such fancy features as native command queuing and hot-plugging of SATA devices. If you leave AHCI off, your drives will run in an emulated IDE mode.

The rub is that AHCI is not supported in Windows XP natively. You will have to use a floppy drive and F6 drivers or create a slipstreamed version of XP with AHCI drivers just to install the OS. If you already have Windows XP installed, flipping on AHCI will prevent the OS from loading. It’s also not clear what level of AHCI support Vista has, but if you install with AHCI on, you don’t need to install drivers. If you install Vista in IDE mode, however, and then turn on AHCI mode in the BIOS, the OS bluescreens.

Do NCQ and hot-plugging make AHCI worthwhile? For the most part, no. NCQ can actually hurt performance in some situations. Still, there have been online reports of chipsets performing quite poorly unless AHCI is enabled. AHCI is supported only by Intel and ATI at this point and not by Nvidia.

 A New Way: UEFI Promises to Make BIOS Tweaks More User Friendly

MSI has already made UEFI available on a limited set of motherboards.

The BIOS is older than many of the people who actually use a PC, so why in this age of 3D-accelerated 64-bit operating systems are we still using a line-based interface and 16-bit real-mode BIOS? That’s a conundrum the industry is hoping to fix with the Unified Extensible Firmware Interface, which may well replace many of the things the BIOS does today. An obvious advantage of UEFI is that it supports a GUI and mouse controls. UEFI would also be processor agnostic, use higher-level languages such as C++ instead of assembly language, and pretty much make booting your PC more like, well, booting a Mac.

It won’t happen overnight, though. Few desktop motherboard vendors beyond MSI have hopped onto UEFI and only the 64-bit flavor of Windows Vista SP1 supports it. Even if UEFI takes off, the BIOS will not totally go away. It’ll just get a serious demotion to doing very basic power on self-tests before handing over control to UEFI. The difference is that you may access those familiar controls using a UEFI GUI interface, which will also roll in pre-OS applications as well.