Turbo boost on i7 - how do I use it?

I have the Core i7 720QM 1.6GHz - the CPU is supposed to be able to disable two cores and run the other two at 2.8GHz. How is this suppsoed to be accomplished?

 

It happens automatically, when needed, and when there's thermal headroom.

 

It does not disable any cores (shutting down cores is possible and done on core i5 and i7 but has little connection with turboboost) and it is used automatically (unless disabled in the bios).
The procesoor has a dedicated circuit inside it that continually calculates power draw, temperature and core load and enables different stages of Turboboost on 1,2,3 or all 4 cores. The more cores have TB active the lesser the frequecy increase.
Turbo boost will kick in more often and at higher values if:
- CPU load is big and not very threaded (the less cores are stressed the higher TB frequency increase - and it's not really random, intel has tables for each processor model just google it)
- The processor has adequate cooling. If calculated TDP approaches predefined values then TB frequencies will decrease so that the system remains fully stable and within specs

In other words the process is fully automatic and hardware level. It's all in the CPU, it does not even require drivers to work. The good part is you can see it in action and even measure how the cpu uses different stages depending on load and number of cores used by running CPU-Z. It will always show you the highest frequency of the cores and you can compare that to nominal frequency and have a little fun testing TB.

 

Try this monitor for the intel i7, its a gadget for the desktop on Windows 7 or the sidebar in Vista.

Scroll to the very bottom and look for the turbo boost monitor gadget:

http://www.asrock.com/MB/download.asp?Model=P55%20Extreme&o=Win7