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Topic Title: Guide to Typical CPU Temps
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Created On: 04/02/2004 04:21 PM
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 04/02/2004 04:21 PM
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I believe this is a fair summary of AMD XP xxxx CPU Temps

AMD64 are a few degrees C cooler.


Government Temperature Warning: Any Attempt to make sense of CPU temp readouts without checking their accuracy can seriously damage your sanity.

The CPU temp sensors on motherbords are highly inaccurate. Readouts are commonly wrong by 20C. Errors as high as 50C have been reported.

1. Safe and Error Free CPU Temps

AMD state the max operating temp for their XP CPUs is 85C. Some earlier CPUS were 90C, but only a few. Stick with 85C.

85C is the Internal Fry Temp. If the temperature inside the CPU goes above 85C you CPU is increasingly likely to die. Permanently.

Most motherboard CPU temp sensors report the Surface temp. The Surface Temp is typically around 10C lower than the Internal CPU Temp under Full Load conditions. So:

Internal Fry Temp = 85C
Surface Fry Temp = 75C

The Error Free Temp is not the same as the Fry Temp. It will vary from CPU to CPU, but typically it's 20C below the Fry Temp, i.e.

Interenal Error Free Temp = 65C
Surface Error Free Temp = 55C

If you overclock your machine the Error Free Temp falls - i.e. your CPU has to run cooler in order to remain stable.

2. Typical Running Temps

As most Mobos report the Surface CPU Temp, we'll stick with that from now on. This has the additional advantage that the CPU heatsink (near the base) is roughly the same temp as the CPU Surface temp, and it's possible to measure the Heatsink temp.

Actual Surface CPU Temps using a standard cooler are typically 30C above room temp on Idle and 40C above room temp on Full Load. You have to be doing something serious to get you CPU temp much above Idle - something that uses 100% CPU continuously. Rendering video, runing Prime95, and some games can do this.

That means that Surface CPU temps on a hot day - say 25C in your room - can get up to 55C, i.e. the typical Error Free Temp. That does not mean the PC will crash, of course; only that it might. Seems about right to me: standard machine, occasional crashes on hot days...

The standard cooler is not really designed for climates where romm temperature goes much over 25C for extended periods of time

With a "top of the range" air cooler the Surface CPU temps will be much lower - 18C over room temp at Idle, and 24C over room at Full Load. So even if room temp reaches 30C the Surface CPU temp is only 54C at Full Load.

This setup is sutable for a heavy duty or overclocked machine.

3. Do I need to worry?

Probably not.

The most important fact in all of this is the 20C buffer zone between Error Free Temp and Fry Temp.

This leads us directly to ActionMan's Axiom:


If your computer is stable it is not over-heating.


Which also means it will crash or shut itself down before serious damage is done.

4. Calibrating CPU Temp Readouts

But if you PC is not stable, and you think heat might be the cause, you need to find out what the CPU temps actually are.

The simplest thing is to measure the Heatsink temp as close to the base as possible. If you don't have a thermometer use this scale:
70C = Burnt Fingures
60C = Painfull
50C = Hot
40C = Pleasantly Warm

Hot is OK as a Full Load temp, anything higher is trouble. Hot on Idle is trouble.

You can also try the Cold PowerUp Test. Like this:

Let the machine cool down (overnight); and switch on, go straight into the bios and check the temps.
At the instant you power on the System and CPU temps should both equal Room temp. Any significant difference is a calibration error in the readouts.

Notice how long it takes for the temp to rise to the Idle Temp. If its around 2-3mins the test is invalid; but if it takes 10-15 mins for the temps to level off, the test is OK. In that case the calibration error is about 2C less than the difference between the CPU temp and room temp at startup.

So why would the test be invalid? Because some Mobos report the CPU internal temp, not the surface temp. The Surface of the CPU is in contact with the heatsink, which acts as (wait for it)... a heat sink; so the Surface Temp reacts slowly. The Internal Temp changes much faster - it could easily go up 15 or 20C in the time it takes to get into the Bios and read the CPU temp.

Finally, you can measure the effectiveness of your CPU cooler.

Take the difference between the Idle CPU Temp (after 15 mins) and the Full Load CPU Temp after running Prime95 Torture Test for 15 mins.

A 10C difference is OK
A 5C difference is excellant.

And you can also calculate your Running Temps using this Difference

Idle Temp = Room Temp + 3 x Difference
Full Load Temp = Room Temp + 4 x Difference

Though on some machines this seems to give figures that are too high.

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