What does it mean to set the cpu's top performance at 60% under a Windows 7 power plan?
I have an intel atom processor at 1.66Ghz, does that mean it will act as underclocked at 1.00Ghz? Or are there other factors to consider?
Very simply: It means that Windows will try to tell your CPU to lower the clock to 1.00 Ghz.
But that's only assuming your CPU supports it; if it doesn't, it'll clock down to the nearest value.
You can use different tools to see how much your computer is actually clocking down:
My answer concerns rather the power-management features of Windows 7, and not the hardware.
Toshiba's How to handle the power managment features of Windows 7 describes the Advanced power settings in the Power Options applet of the Control Panel:
The mentioned Microsoft document can be found here : Processor Power Management in Windows 7, which also mentions :
Processor Clocking Control
Windows is using Intel's SpeedStep feature to do this. Intel has a full explanation of how SpeedStep works on their website. The Wikipedia article is also very informative. I don't know what more specific information you're looking for than what Sandeep already told you, but one of those sources likely has it. Intel's Atom Processor info page might also have the info you're looking for somewhere in their technical documents.
Most if not all CPUs have power saving features, Intel with Speedstep and AMD with Cool n Quiet, which can be enabled/disabled in the BIOS (most likely not being able to be changed in laptop BIOS)
setting your processor at a max of 60% in the speed setting will set it to 60% of the actual speed of the CPU.
Each stepping from 0-100% has voltage changes, therefore sticking your CPU to 60% will underclock your CPU and also provide a lower voltage than used in the max CPU clock thus saving power.
Looking here: intel.ly/6Gm0EV -- It shows that it's voltage ranges are 0.800V-1.175V I have tried having a look around the net but I can't seem to give you exact information about the steppings of speedstep. You can try booting into a live ubuntu CD and entering "cat /proc/cpuinfo" into a terminal to see what it outputs.
Hope that helps.