When I say Linux allows for higher overclocks I mean yeah, faster. Windows puts a lot of heavy tasks on the CPU before you even begin and due to it's kernel (the base part of the operating system that understands your processor, x86 for 32bit and 64 bit for, well, 64 bit) being incredibly fussy if you push your CPU too far it will crash, be unstable, poop its pants etc. Linux is a lot less fussy about 100% CPU function and thus allows you to run a higher overclock and it to remain stable.
The frontside bus is how your CPU takes its base speed. Let's assume here that you have a Phenom 2 940 3ghz stock settings processor. The way it will work is like this....
FSB = 200mhz (remember, these are just examples and not exact sciences !)
Multiplier = 15x.
15 x 200 = 3000 (3000mhz or, 3 gigahertz).
Now. On a regular AMD and regular Intel CPU they come at their stock speeds and when you fit them into your motherboard, so long as the board supports them, the motherboard will automatically detect your CPU and set it to the speed the CPU wants to be at stock.
Now. AMD do a CPU called a black edition. With this CPU the multiplier will auto detect and set and so will the FSB. However, to overclock all you need to do is set the multiplier from Auto to Manual and then you can increase it. So as an example for me to reach 3.4ghz with my 3ghz CPU all I need to do is feed it more multiplications of 200mhz. Like this...
Phenom 2 940 stock settings
FSB = 200mhz
Multiplier as stock = 15x
15 x 200 = 3000 (mhz).
My overclock
FSB = 200mhz
Multiplier = 17x.
17 x 200 = 3400 (mhz) or 3.4ghz.
Now. I am at stock voltage for my CPU. I can't remember what that is now but google is your friend. Thing is, if you push too hard the CPU will become unstable. You can increase the voltage but doing so can make your edge transitors in the CPU become fuzzy. And instead of feeding 0's to the kernel in Windows they will then feed say, 1's. At which point if one of those occur Windows will either crash, become unstable or, in worst cases, die (your install will become corrupt).
Remember the above applies to a CPU that is either AMD black edition or Intel Extreme edition.
If you do not have an AMD black edition CPU then your multiplier is locked. There is then no way to increase it to make the CPU go faster. So, all you can do then is increase the frontside bus which works like this.
Let's say you have the same CPU (A phenom 2 940) but you did not have a black edition. You would then do something like this.
FSB = 220
Multiplier 15x ( locked )
220 x 15 = 3300 (mhz, or 3.3ghz)
And so on. However, increasing the front side bus usually needs more voltage to the CPU than when you are just fiddling with the multiplier.
I made a post about CPU manufacturing before, but usually the black editions are the better more stable CPUs of the run. At which point AMD will leave the multiplier unlocked and charge a little bit more for the CPU.
Intel on the other hand? well, they leave the multiplier unlocked and then rape you in the bottom.
If your AMD is not a black edition then you will have no other way to overclock it than using the FSB, and, that is a lot harder to do and more complicated than simply increasing the MP (or multiplier).
HTH !