> Have you participated much in the overclocking community? The whole point is that every CPU chip is different and can be overclocked by different amounts, some almost not at all.
On the other hand, there is no way that you can actually determine how far a CPU can be overclocked and still maintain full functionality, so it might be best to limit overclocking to systems that will not be used for something of high financial or safety value.
The problem is that fundamentally the hardware is still analog. Digital is an abstraction on top of the underlying analog system. In the digital abstraction, a signal changes instantaneously from 1 to 0 or from 0 to 1. In the underlying analog system, the components carrying the signal have capacitance and resistance. Changing the high voltage that represents 1 to the low voltage that represents 0, or vice versa, involves discharging or charging that capacitance through that resistance, and that takes time.
This sets an upper limit on how quickly that signal at that particular point in the circuit can change digital state.
There are also other ways the analog nature of the underlying circuit leaks into the digital realm. Neighboring components that are in the digital abstraction completely isolated from each other (except through intentional connections) might be coupled by stray capacitances and inductances. This can let signals on one cause noise on the other, or the state of one could change how fast the other can change state.
When a chip is designed the designers can figure out what areas are the most vulnerable to potential analog problems. They can incorporate into their tests checks to make sure that these areas are OK when the chip is operated in spec.
The ideal scenario is that if you clock a chip fast enough to break something, the chip blatantly fails and so you find out right away, and can slow it down a bit.
The frightening scenario is a data dependent glitch, where you end up with something like if the ALU has just completed a division with a negative numerator and an odd denominator and there has just been a branch prediction miss, then the zero flag will be set incorrectly.