Different p-states will let processor core work at different frequency level and voltage level. It's enabled by Intel Enhanced Speedstep technology.
I want to do some power management research(on Xeon since it has at least 4 cores on a socket). However, different processor's p-states capability is very different (for example, some processors will only have 2 p-states while others will have more). I know how to check it on the machine. But does anyone know if there is a place showing all the information for all Intel processors? So I can figure out which processor I am going to buy. I can not find such information on Intel's website.