Why do people underclock their CPU?

[basedthirst]

Why might one underclock a CPU, wouldn't it just run slower?

[Kenji the Uke]

Probably cooler temps 3: 

[itsmyjobtoknow]

I wouldn't know why someone would underclock a CPU on a desktop, but for mobile devices, it is a viable option to obtain a longer battery life. 

[King_of_Oz]

It's not underclocking, it's underVOLTING. Undervolting it the act of using the mobo BIOS to reduce the amount of power the CPU needs, without doing it enough to reduce preformance, to make the system consume less power. This can be done beacause the manufacturer of the CPU usually lets the CPU more power than its needs, to allow headroom.

[Wlllllll]

If your running a desktop pc people don't really do but on a laptop becuase lower temps and better battery life.

[Wlllllll]

2 minutes ago, King_of_Oz said:

It's not underclocking, it's underVOLTING. Undervolting it the act of using the mobo BIOS to reduce the amount of power the CPU needs, without doing it enough to reduce preformance, to make the system consume less power. This can be done beacause the manufacturer of the CPU usually lets the CPU more power than its needs, to allow headroom.

That's not right at all. unlocking is both unlocking and undervolting.

[Levent]

anything that runs too hot or runs on batteries benefit from underclocking along with undervolting.

[King_of_Oz]

1 minute ago, Wlllllll said:

That's not right at all. unlocking is both unlocking and undervolting.

But you can reduce the voltage without reducing the clock speed. It is true. I read it in a MAXIMUMPC magazine, which I think is a reliable source. But, you can also reduce clock speed, but this practice is not commonly done on desktops.

[PianoPlayer88Key]

I remember underclocking a desktop CPU once for stability reasons.

 

My dad's old Athlon 1.4 GHz, back in early 2008, had gotten to where it would shut down after only a few minutes or so of use, making it almost unusable.  (I forget if it would BSOD, or just power off.)

 

I underclocked it to 1 GHz in BIOS (900 MHz wouldn't boot), and was able to use it for about 20-30 minutes at a time.  Between a few sessions, this was sufficient to allow me to order the parts for my own first PC, which included an Athlon 64 X2 4000+.  (I wish I could have gotten something like a Q6600, but I was on a <$500 budget.)

[typographie]

57 minutes ago, basedthirst said:

Why might one underclock a CPU, wouldn't it just run slower?

You generally wouldn't, unless maybe you were trying to squeeze a little bit more life out of a slowly dying CPU.

 

Most modern CPUs will clock themselves up and down depending on what kind of work they're being asked to do to be more efficient and to let the fans quiet down when possible (assuming you didn't turn that off), but that's just basic functionality.