Overclocking of modern
PCs is usually done by increasing either the
motherboard's bus-speed, or the
clock multiplier of the
processor. This can be done directly either with DIP-switches on the motherboard, or if you have a more fancy (iow expensive) motherboard, from the
BIOS. This is done until the point the
computer stops working, after which it is set to the last stable speed, and presto, you suddenly have a faster computer without forking out any money.
Of course the processor runs at higher temperatures when its operating at higher speeds, so you can add some more effective cooling if the speed you get with normal fans isn't enough for you.
Cooling people usually use for this purpouse includes
peltier-elements, water-cooling, old freezers and other crazy stuff.
If you want a new processor that is very cheap, buy a
AMD Duron 600
MHz, it costs practically nothing, and is almost always overclockable to at least 850MHz, even with standard cooling, if you are the type who doesnt want to fork out a fortune for a new computer, and aren't afraid of playing with your
hardware...