Hardware Reference
In-Depth Information
which is 128MHz faster than the rating. This took all of about 60 seconds to reboot, enter
the BIOS Setup, make the changes in the menu, save, and reboot again. This was only a
4% increase in overall speed, but it didn't cost a penny, and testing proved that the system
was just as stable as it was before.
Many motherboards allow changes in speed of up to 50% or more, but a processor rarely
sustains speeds that far above its rating without locking up or crashing. Also note that,
by increasing the speed of the processor bus, you may also be increasing the speed of the
memory bus, PCI bus, or PCI Express (or AGP) bus by the same percentage. Therefore,
if your memory is unstable at the higher speed, the system will still crash, even though
the processor might have been capable of sustaining it. The lowest common denominator
prevails, which means your system will run faster only if all the components are up to the
challenge.
Overclocking Pitfalls
If you are intent on overclocking, there are several issues to consider. One is that most
processors sold since 1998 are multiplier-locked before they are shipped out. Processors
that are locked ignore any changes to the multiplier setting on the motherboard. Although
originally done to prevent re-markers from fraudulently relabeling processors (creating
“counterfeit” chips), multiplier locking has impacted the computing performance enthusi-
ast, leaving tweaking the motherboard bus speed as the only easy way (or in some cases,
the only way possible) to achieve a clock speed higher than standard.
Tip
Intel's K-series Core i7 and i5 processors have unlocked clock multipliers, as do AMD's
BlackEditionPhenomII.Phenom,andAthlonX2processors.Choosetheseprocessorsalong
with a motherboard that offers adjustable clock settings in its BIOS for easy overclocking.
You can run into problems increasing motherboard bus speed as well. Most older Intel
motherboards,forexample,simplydon'tsupportclockspeedsotherthanthestandardset-
tings. Some newer enthusiast-oriented Intel boards have “burn-in” or “override” features
that allow you to increase the default processor bus speed (and the speed of the processor
core), voltages, and multiplier (for unlocked CPUs). Most other brands of motherboards
also allow changing the bus speeds. Note that small incremental changes in clock mul-
tiplier speeds, rather than large jumps, are the best way to coax a bit more performance
out of a particular processor. This is because a given chip is generally overclockable by
a certain percentage. The smaller the steps you can take when increasing speed, the more
likely that you'll be able to come close to the actual maximum speed of the chip without
going over that amount and causing system instability.
