It’s not stable by any means, but a group of Finnish overclockers have got a 3.6Ghz Pentium 4 up to 6009.73Ghz. The chip needs liquid nitrogen to keep it running, so don’t try this at home – it’s not available as a home system, and doesn’t even fit in a case. Though non-toxic and non-flammable, liquid nitrogen does present a frost-burn and asphyxiation hazard to geeks who have to calculate PI just that bit faster.
For safety, he overclocked system has low memory and a cheap graphics card, so has a couple of key performance bottlenecks (after all, you wouldn’t want to risk destroying a nice new Radeon X800 if you fried your system board), but is an interesting proof of concept. In this instance, only program that run entirely on the processor and do not make memory, disk and graphics calls with show the most benefits from this level of overclocking.