I set my iMac up last night to burn an hour and a half long DVD with iDVD, so I knew it was going to take at least two or three hours to encode. Even working off of an external hard disk, the CPU temperature immediately shot up to a consistent 195 degrees. Having had a Rev. A iMac that had both a fried hard drive and logic board, I'm pretty sensitive to the operating temperature of this machine. Not wanting to leave the machine running at that temperature for such a long time, I went to system preferences and set the processor performance to "reduced." Immediately the temperature dropped to a steady 165-170 degrees. My question is, what technically happens when you reduce the performance? Does the chip downclock itself? I'm just curious as to how exactly the process works. Wondering if anyone might know.