CPU Usage

rmg1

Hi all

Bit of "because I don't know" type question this one.
What happens if you run a CPU at 100% for extended periods?

Will it fail or does the mahine it's running on just shut down until it cools down?

If it's the latter, what happens if you keep doing it?

Guardsman

What causes your CPU to run at 100%

John_Gray

rmg1 wrote: »

What happens if you run a CPU at 100% for extended periods?

"Nothing much," would be the best answer (for at least two reasons!).

A CPU should have an adequate cooling fan, so that will be running continuously. A CPU should be able to run at 100% for ages, but in normal circumstances a program would rarely require this.

Obviously 'some program' (or something looping) will be using the CPU to cause it to run at 100%, so other programs won't get too much of a look-in. Windows will try to spread the load, though, but everything else will probably be sluggish.

Think of a car engine running at full throttle. You wouldn't want to do that for too long, but it's not likely to cause much in the way of problems. A CPU would have even fewer problems!

So what have you broken?!

rmg1

Guardsman - This was just a rhetorical question really, I was just curious.

John - Thanks for that, and I haven't broken anything ..... yet.

Ectophile

Most PCs these days have automatic fan speed control. So if you run at 100% CPU for more than a few seconds, the fans will speed up and the PC will get noisier. It will also use more electricity.

Provided that your PC isn't full of fluff, and the fans were properly specified for the job, then that's all that will happen.

esuhl

I'm fairly sure that CPUs are designed to be capable of operating at 100% load 100% of the time. The problem is likely to come from inadequate cooling (due to fans, case design, improper thermal contact between the CPU and heatsink/fan).

Old CPUs had no thermal cut-off feature, so extended overheating would result in the CPU being physically damaged. Intel introduced this feature quite a while before AMD, IIRC.

Modern CPUs (from around 10 to 15 years ago to the present) generally had some kind of thermal cut-off, so the PC would shut down to prevent damage if the CPU overheated. And, as Ectophile says, fan speeds could adjust dynamically according to CPU temperature.

I might be wrong, but I vaguely recall reading something about even more modern CPUs using throttling to cope with overheating. So when the CPU is under full load and overheating, the speed (and voltage, etc.) of the CPU is reduced (so it operates slower and generates less heat) whilst still maintaining 100% load.

(This is all off the top of my head from distant memory, but I think that's vaguely correct.)

Johnmcl7

It should not be an issue for a processor running at 100% constantly as the processor's cooling is chosen with this maximum heat dissipation in mind. Modern processors have complex thermal systems which allow them to dynamically overclock and underclock themselves depending on their load and their running temperatures however in the worst case if the processor is unable to keep itself from running too hot the system will shutdown. Usually if you attempt to power up the system immediately after, the PC won't start as it's still too hot and will only start when it's had time to cool down although since this is caused by a cooling failure (a fan clogged up with dust or a failed fan) it won't last long before it powers back down again.

I have really hammered some processors with long sessions at 100% (through gaming or video encoding) and they've been fine, the only ones I've had trouble with were some of the old P4's in ultra-small form factor PCs as they simply weren't suitable for that. A lot has changed since those days though.

John

rmg1

Thanks folks
This is an actual scenario on one of our servers that has far outlasted it's usefulness (it was a temporary solution 5 years ago). They won't spend money on a new one (or even upgrading this one) so I was trying to justify the spend based on the "it's going to go pop" routine.

Looks like I'll have to come up with something new on that one.