My PC spec: I'm not planning on changing the hardware, partly because I'm happy enough with it and because of a tight budget. The board has a bug that ASUS are being quite obtuse about, so I guess I'll have to accept the status quo. When this board resumes from standby/S3/sleep, the undervolting setting I've set in the BIOS is forgotten about until the PC is either restarted, cold-started or resumed from hibernation. I use the computer several times a day, and perhaps for hours at a time, or if I'm out on appointments I might use it several times a day for only say an hour on 2-3 occasions. The undervolting setting isn't much, but it is the maximum under-volt setting that the board's options will let me choose. When I had all six cores enabled, here's the power usage stats: -0.06v offset: 85-90W idle, 175W load standard: 89-95W idle, 186W load My feeling is that 5W saved on idle isn't much, but over a year if it saved a fiver it's better than no saving at all. However, the power usage penalty of resuming from hibernation three times a day might offset that. This is really the crux of my question. When a computer starts up (I imagine hibernation and a cold start are fairly similar in terms of their demands power-wise), the processor is cranked up quite a bit until the system finishes booting. Currently I've got the computer going into hibernation after an hour of idle time (I'm not sure why I changed it from 45 minutes to an hour now, as 45 minutes, but anyway). The advantage of going back to using S3 sleep is obviously that it resumes a heck of a lot quicker - (5 seconds versus 30 for hibernation), and probably uses less power to resume from sleep than hibernation.