The CPU's clock speed is the FSB clock speed (base, not effective speed) times
the CPU's multiplier. On most newer CPUs, the multiplier is locked, so you will
have to adjust the FSB clock speed (However, it might be possible to 'unlock'
the chip's multiplier on some older chips. See CPU Locking.) The FSB is not
adjustable on some motherboards, and almost all OEM systems. The FSB and
multiplier, if not locked, are adjustable from within the BIOS. Note that upping
the FSB clock speed also increases the clock speed of many other components,
including RAM.
When increasing the FSB clock speed, do so in small increments of a few
MHz at a time. After you do this, boot up your computer to make sure it works.
If your computer successfully boots, increase the FSB some more. If it won’t
boot, lower the FSB until your computer properly boots up. Repeat until you
have the highest setting with which your computer will boot up. Next, test your
OS to make sure it is stable by running a burn application, or any application
that uses 100% CPU power. If a crash or reboot results, lower the FSB speed
some more until it runs smoothly. On some motherboards you are also able to
change the voltage of the CPU and other components in order to help stabilize
the system. However, this increases the components' heat output and can harm
or shorten the life of your system instead.
Notes: On AMD K8-based chips (Athlon 64, Opteron, Turion, and Socket
754 and 939 Semprons), there is no FSB- there is an integrated memory controller
(IMC) and a HyperTransport bus (HTT). The IMC has a base clock
speed like a FSB does and for overclocking, it would be adjusted just like a
FSB would. The HTT can also be overclocked like the CPU core can be. Its
base clock speed is the exact same as the IMC's and thus by default you will
overclock the HTT bus as you overclock the CPU. Note that the HTT bus has
a multiplier and it is adjustable. Many motherboards do not function well with
the HTT bus frequency much over the stock frequency- that’s where the adjustible
HTT multiplier comes in. (It should be noted that overclocked systems
are most stable when the HTT is at or below 1000Mhz)
Also, some newer desktop processors (AMD K8 series with Cool ’n Quiet,
Intel Pentium 4 6xx series, Pentium D 830, 840, stepping C1 Pentium D 9xx series
with Enhanced Intel Speed Step) and most mobile processors (exc. Celeron
M) can vary their operating frequency while running by lowering the CPU multiplier.
This results in multipliers below the highest one being unlocked. This
allows for a very high FSB/base clock speed with a lower multiplier to use very
fast RAM to its full potential without overclocking the CPU so much that it is
not stable.