I usually keep my PC on for 24/7 and most of the time this damn things remains IDLE. I was wondering if PC's could be underclocked. Well, if It could then may be it can help the processor to be cool, consume less power as well as increase the life of the processor too.
But I haven't heard anywhere of UNDERclocking as such, just a question.

You can 'underclock' a CPU in the same way that you would 'overclock' it - just fiddle with the settings, switches, and jumpers. Whether or not it works on all CPU's, and whether or not it actually reduces the work load I don't know, but it can make your processor be reported as being slower.

Started another Topic for Cooling processors.

With the new generation of AMD processors, when you don't use much of the system, the processors switch to a lower coefficient number. So when you use your CPU much, it remains at the his normal speed and voltage. When you have a lower CPU usage, he switches for example to 800Mhz instaed of 2000Mhz. That reduce the consuming, and it increase the life of the processor.

Of course you need to by a new CPU to do that this way. But I think Speedfan can do that, it can easy overclok and so maybe underclock your CPU to.

You can have Speedfan for free here:

Speedfan homepage

I think its a bad thing, that feature is usually reserved for mobile processors. Its bad for a desktop as it will reduce performance sometimes. You'll also get "the dust problem" I think.
Anyway you can't underclock a CPU. Even if you did, it would consume the same amount of power so its useless.
If you want a computer that runs cool get a Celeron or a Cyrix 3 based system. Though I highly not recommend either of them especially the Cyrix 3.
If you still want a computer that consums a bit less power, you can also opt for a laptop.
For example, the power supply on my sis' desktop is rated at 140W as in my laptop, it consumes only 90W.

The Pc can be underclocked, check http://www.cpuidle.de/

CpuIdle is a CPU cooling and power management software.
CPU cooling will help you achieve these things:

* decrease CPU temperature
* enhance stability
* enable overclocking (overclocking increases temperature- CpuIdle gives additional headroom)
* increase CPU life (a decrease by 10°C doubles the life span)
* cut power consumption

CpuIdle uses several mechanisms to keep your CPU cool:

* shutdown CPU when not used (online cooling)
* optimize CPU for maximum cooling effect
* optimize chipset for maximum cooling effect (supported chipsets only)

most of the newer Microsoft and all of Linux OS, use the halt command when CPU is in idle loop. This effectively slows down the clock and cools down the CPU. I know this for sure by actually monitoring CPU temperature externally.

Can I ask something? why would you want to cool a CPU? I would understand if you owned a mobile device like a tablet PC or a laptop. Cooling would be a big issue because the CPU fan eats up a lot of power. But I mean... you own a desktop... unless if its like extreme heat 40-60 degrees celcius why be worried?

Meh, I'd prefer to OVERclock my processor, only if I had the right power supply to run it after that and could keep the heat temperature in there low enough so everything else don't get burnt out.

Underclock is just to low the FSB freq.