Most Intel PCs and Laptops are over clocked by swapping out the CPU because the clock circuitry is in the CPU itself. So unless the CPU is on a socket and not soldered to the board, this should be simple fix. Like on the Mac Mini with the Core Single/Duo Intel series, swapping out the CPU with a Core 2 Duo (7200, 7400 or 7600) will upgrade the system to true 64bit Dual Core CPU at 2.0 to 2.4 GHz.
However, in a lot of systems the CPU is soldered to the board, mostly laptops. There is little one can do here. But in NetBooks using the Intel Atom CPU, there is some hope; like the Raspberry Pi, the clock is software switchable though this is not "advertised" to the outside public world. Thus you can take a 1.6GHz NetBook and boost it up to 1.86GHz or if you got the balls - to 2.1GHz.
The problems with this, like on the Raspberry Pi and other Pi Systems, is that the system gets very hot. And since laptops run on batteries most of the time, the batteries run down faster. So though this is a software mod, some hardware mod is needed to make it go better: clean out the cooling fan inside the NetBook, if you can, remove the CPU Heat Sink and clean the heatsink good off it and replace it with a dab of "Silver Arctic" Heat Sink paste. And check and replace your (Slow) RAM. If your RAM is Slow, it will drag down the system, so replacing it with faster RAM will speed things up. But this is only if your system has a taken a large speed jump (see below).
This is a working Hack, a hack that works but you need to know your stuff: What system, what CPU, etc. This video only shows the Atom 450 CPU but it applies to other Atom CPUs as well. And like the video says, takes it a bit at a time. Ramping it up all at once to get the high speed may not work on some machines, so try out the lower faster settings first and see what the machine can handle.
This mod is software based (like on the R-Pi's). And you can change it back. You need to download some software that adjusts both the CPU Clock and the Data Bus Clock Speed, and then play with the settings of the CPU to see what works with it. Intel says that the Atom can handle the higher speeds but that depends on how the system can remove the heat.
All the instructions are in the video link:
https://www.youtube.com/watch?v=KYP285X0iEM