cpu throttling--what is it?

[Luca Pireddu <lucap@shaw.ca>]

Could someone explain to me (or point me to where I can find an answer) what 
CPU throttling is?  My sony vaio has 8 CPU throttling levels:

$ cat /proc/acpi/processor/CPU0/throttling
state count:             8
active state:            T0
states:
   *T0:                  00%
    T1:                  12%
    T2:                  25%
    T3:                  37%
    T4:                  50%
    T5:                  62%
    T6:                  75%
    T7:                  87%

I see that varying the setting has a big effect on performance (and presumably 
battery life).  However, the throttling setting doesn't seem to affect my CPU 
clock.  So how does it work?

Thanks

Luca