What is CPU Idle Temperature?
What is CPU idle temperature and why does it matter at all? Well, it doesn't, really, but it's best pal the CPU load temperature is going to be a frequent visitor at your monitor if you ever have a problem with random shutdowns or happen to overclock.
Idle temperature is the temperature reached by any chip that acts as a heat source. CPU is one of the biggest guys in town, not only in terms of heat generation but price, too. So yeah, it makes just a little sense to have an idea about its idle temperature.
Let me start with a little story here about a laptop I had to repair the other day. It was shutting down randomly and the owner told me she suspected the battery. I knew that it was the processor, but you can't tell that to people just like that, now can you. They'd freak out. OMG, the processor is going to die, how much does that cost, I'm so throwing this <censored> out!
That's why you don't tell them that the processor may be overheating.
The root of the problem wasn't the idle, but the load temp, but I had to check everything to know that. While doing nothing this Sempron 3300+ AMD CPU was about 55C(131F). Nothing odd but I thought it was a little high even for a mobile processor.
The problem was that when the single core started to churn out some processed data it quickly reached 85C(185F) where the electronics shot it down without asking or mercy. The problem wouldn't have been so severe if the basic temp was something more manageable, 35-40 celsius tops. Also, 55C as idle didn't really look normal to me, but it wasn't what I'd consider clinical.
I took the whole thing apart and noticed that when I would spread thermal paste on it, only half of it would touch the heatsink. You can't do much about that in a notebook because everything is milled to the fraction of a millimeter. The solution I found was to put two pieces of folded paper under the springs where the bottom didn't touch the die.
It worked wonders and the idle temperature dropped to 48C, while under load it never exceeds 77C. I found that out running priority 9 Small FFT Orthos for four hours on it. The other trick I tried was to lower voltage with RightMark's CPU Clock utility to the point where it's still stable in Orthos even after longer periods.
It lowered both idle and load temperatures, so I called it a day. It's been working ever since.
CPU idle temperature doesn't really matter as long as it's under control when in load. To directly answer the question in the title (I wonder how many of you get this far!): CPU idle temperature is how hot the processor is while doing absolutely nothing apart of basic operating system tasks.
Another neat trick I've learnt to measure temperature of the processor is to touch it. 'There is a big fat heatsink on top of it, how could I touch it?' could you ask, and that's a fair question. Touch the bottom of the heatsink then. Be very careful, an 8cm diameter fan can easily cut your finger and anything above 60C(140F) hurts a lot.
Here is how you do it: Touch the base of the fins and if you can keep your finger there for at least 10 seconds, it's definitely under 60C(140F). If it feels cold, it's under 35C(95F). Add about 10-15C to that and you've got the core temperature(no thermal connection is ever perfect, there is going to be power lost between the core and the heatsink).