As Goes Voltage, So Goes Speed
Hack #26 from PC Hacks by Jim Aspinwall (O'Reilly Media).
Adjusting the power supply voltage to your CPU can make all the difference between an erratically performing speed-hack and a stable screaming demon.
Overclockers love to tweak every available parameter in attempts to squeeze every bit of performance out of their CPUs and system boards. Cranking up the speed is the most obvious way to get the CPU to run faster, but to get or keep it running at higher speeds you may have to jack up the CPU's power supply voltage a notch or two.
Today's CPUs run at extremely low voltages–in the range of 1.3 to 1.9 volts. As the CPU runs faster it gets warmer; as things get warmer their resistance increases, which causes loss of voltage and limits the available current to keep the device powered adequately. At these low voltages, it does not take much resistance to have a significant impact on voltage drop and increased heat generation.
Also, when the CPU runs faster the data signals tend to get a bit weaker, so increasing the voltage gives the data signals a little extra edge in getting through to the other components.
WARNING: Be very careful with this hack; if you give the CPU too much juice, the internal temperature will rise quickly until the CPU components burn out and quite possibly release all of the "magic smoke" (and real smoke), rendering it useless. Ensure you have an adequate heat sink properly bonded and securely fastened [Hack #24] atop the CPU!
This is where you really need to check the BIOS CPU temperature alarm settings, if provided, and make sure they are enabled, or monitor CPU temperature with Sandra or a similar utility.
CPU voltage control may be available within your BIOS setup program, jumpers, or switches on the system board. Voltage adjustments may be in increments of 0.025, 0.05, or 0.1 volts, depending on design.
The common procedure for CPU voltage hacking is, at the CPU's rated speed, first try the next higher voltage increment than the default for your CPU. For example:
- If the default is 1.3v, step it up to 1.325v and turn the system power on. If the system starts, boots up an operating system, and runs flawlessly for several hours, no damage has been done so far.
- If the system passes the voltage increase test, begin increasing clock speeds until the system fails or becomes erratic, then back down to the last stable speed setting.
Repeat these steps until you crank it up as high as it will go while still maintaining stability. This seesaw setting method should allow you to get the clock speed up a bit higher. For common CPUs, the voltage limits are:
- Slot A AMD Athlon Classic: Max of 1.9v
- Slot A and Socket A Athlon Thunderbirds: Max of 1.85v
- Socket A AMD Duron: Max of 1.85v
- Intel Pentium, early Pentium II: Max of 2.8-3.3v
- Pentium II, early Pentium III (<600 MHz), Celeron: Max of 2.0-2.12v
- Pentium III (>600MHz): Max of 1.6-1.69v
- Pentium 4: Max of 1.6-1.85v
Do not increase the CPU voltage greater than its published operating voltage unless you can afford the risk of damaging and having to replace the CPU–sometimes an additional 2-5% performance increase is not worth the $80-300 for a replacement CPU. At those prices you can buy a faster system board and CPU combination.
This material has been adapted from PC Hacks by Jim Aspinwall, published by O'Reilly Media, Inc. Copyright O'Reilly Media, Inc., 2004. All rights reserved.
Covering both Windows and Linux, PC Hacks combines the bestselling Hacks series style with the world's most popular computing hardware. Hacks for enhancing performance and preventing problems with your PC include overclocking CPU and video cards, tweaking RAM timing, selecting the best performing components, and more. The guide includes advice on reusing an old PC to off-load work from newer systems as well as ways to prevent security hacks.