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Old 2010-09-04, 12:26   #1
yamayamayama
 

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Default Is 100% cpu usage normal?

Hi,
A few hours ago I install prime95 on window 7 32 bit
I left all the default settings ( see attachment )

Is there any chance of damaging my computer?

thanks in advance
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Old 2010-09-04, 13:57   #2
retina
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100% is normal, and expected.

As for damage, well your cooling system might have to be monitored for signs of wear, but otherwise there is unlikely to be any damage.
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Old 2010-09-04, 14:01   #3
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Default CoreTemp

You can check your CPU temps for example with a prog called "CoreTemp". Cooler is better but no need to worry until 80° Celsius. Have a look for "TJmax" - the max. allowed temp for your CPU. Often at 99°C but not always.
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Old 2010-09-04, 16:04   #4
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Default How about older PCs?

Quote:
Originally Posted by Brain View Post
Cooler is better but no need to worry until 80° Celsius.
Brain,

Do you know if that applies to all computers (including older ones made 10-15 years ago), or mainly to modern computers (built within the last 2-3 years)?

Rodrigo
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Old 2010-09-04, 21:18   #5
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If you think that CoreTemp's 100C is the limit, you will be unpleasantly surprized when the magic blue smoke comes out.

There are special thermal specs that are different for different CPUs. Find official specs for your CPU on the manufacturer's site. For Phenoms, for example, see here, 62C is a recommended limit. Surely, you can go higher. The question is for how long.
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Old 2010-09-05, 09:56   #6
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Default Attend the specs

You should always attend the CPU's thermal specifications. I don't know how older CPUs behave. 80°C is hot already = yellow traffic lights. Look for "Electromigration" in wikipedia. As far as I know, this problem scales linearly with temp. So double hot, half CPU lifetime. If it was 10 years, you drop to 5. But as long as you don't overclock, 100% CPU usage should be no problem. Thermal cooling is designed for that.

There are other threads here handling this topic in more detail.
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Old 2010-09-05, 22:44   #7
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Quote:
Originally Posted by Rodrigo View Post
Brain,

Do you know if that applies to all computers (including older ones made 10-15 years ago), or mainly to modern computers (built within the last 2-3 years)?

Rodrigo
As Brain said, check the thermal specifications for your particular model.

Different circuit and CPU architectures will throw off differing amounts of heat. Different cooling setups will vary in effectiveness. Reputable system constructors will install a cooling system adequate for the particular CPU in that system; others may not.

If your CPU's specs say the safe thermal range is up to 65 C, then it's irrelevant whether 80 C is okay on some other system.

On my own desktop system, when I start prime95 I hear the cooling fan speed up one step above what I hear for an idle system. As weeks pass (and dust accumulates inside the case), I begin hearing the fan speed up another step for a few seconds then step down again. When it reaches the point of almost always staying at that second speed, I shut down and clean out the dust.

Last fiddled with by cheesehead on 2010-09-05 at 22:50
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Old 2010-09-06, 04:15   #8
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Newer CPUs clock down if they are getting too hot. My Q6600 Quad is running at 80 C for over 4 years now.

Not that you need to run at that high temperature but it's not a problem if you want to do it. As long as you don't play around with the core voltage in an extreme way the chance to burn your cpu is none to zero.

Last fiddled with by joblack on 2010-09-06 at 04:18
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Old 2010-09-06, 04:38   #9
mdettweiler
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Quote:
Originally Posted by joblack View Post
Newer CPUs clock down if they are getting too hot. My Q6600 Quad is running at 80 C for over 4 years now.

Not that you need to run at that high temperature but it's not a problem if you want to do it.
I'm not so sure they actually clock down per se; I think thermal throttling slows it down some other way. My CPU (C2D E4500) is overdue for a vacuuming-out and has been running at 83-84 C for a week or two (compared to a thermal spec of 72 C), yet according to CPU-Z it's still running at the nominal 2.2 Ghz.

Note also that thermal throttling doesn't actually prevent damage in and of itself; all it does is "apply the brakes" a bit to keep the temp from rising too quickly. With enough dust accumulation, a CPU can get up to very high temperatures and risk electromigration despite thermal throttling.

Using my CPU as an example, I would probably be OK running it at 75 C long-term; but I would expect that running at >80 C for extended periods would risk long-term damage to the CPU. This is more of a gut estimate than anything, though Brain's mention of electromigration would seem to support the idea that it's around that point that most modern CPUs begin to be damaged over the long run. Note that my CPU's absolute limit at which it shuts down the computer to prevent immediate damage is 85 C--the high end of the "long term danger zone".

A more tangible effect of increased CPU temperatures, though, is that thermal throttling seriously cuts their speed. The effect is quite pronounced on distributed computing applications, though in my experience it can make general operation of the computer seem more sluggish as well. Thermal throttling cuts in at the thermal spec value (72 C in my case) and increases in magnitude as temperatures get higher. (Returning to the brakes analogy, it's like seeing an obstacle a ways ahead, applying the brakes a little, realizing that you're still going to run into the obstacle, and pushing the pedal increasingly harder as you near it.)

What I do is run a temperature-monitoring application (RealTemp or Core Temp) in my system tray at all times and watch as it gets higher--when it gets over 75 C I make a mental note to vacuum out the computer at the earliest convenience. (Which usually means that it's bumping up against the 85 C limit by the time I get around to cleaning it. ) For computers that I don't have regular access to, I keep a copy of RealTemp or Core Temp on them and check it periodically.

In short (primarily to the OP): CPUs are supposed to be designed to be able to run at 100% all the time. So Prime95 is not making the computer do anything that it's not supposed to be able to do. Most professionally manufactured systems (as well as home/semi-pro built systems that were done right--for instance, no overclocking on a stock CPU cooler) should be able to handle the heat, as long as you keep them reasonably free of dust. Dust is really something that's good to watch even if you're not running Prime95, but it's not quite as crucial a problem if the CPU is mostly idle.
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Old 2010-09-06, 04:49   #10
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Thermal throttling is usually just skipping a subset of clock pulses. So a 2.2GHz clock is still running at 2.2GHz but the CPU will only be allowed to progress on some of the clock cycles.

As for electromigration. I think the effects are being overstated here. It is a very slow process, requires very specific conditions and is proportional to the voltage. The low voltages in modern CPUs reduces the effect markedly. I seriously doubt that anything less than 10 years (and more like 20 years+) will have any affect on the CPU operation even if one operates the core permanently at 100C.

Last fiddled with by retina on 2010-09-06 at 04:54 Reason: Clarify
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Old 2010-09-06, 05:10   #11
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My thanks to Brain, cheesehead, joblack, mdettweiler, and retina for a most informative discussion!

I'm using CPUID Hardware Monitor on one of my PCs. It's an inexpensive, refurbished P4 that I recently bought specifically for use on GIMPS. (It's doing double checks.) For the first week or so, according to CPUID-HW the temperature would quickly rise to 58-59C and stay there after launching Prime95, with the fan whirling at 2100 RPM or so. A couple of days ago I did some Windows security updates and had to restart the computer, and now it's not getting above 36C and the fan's steady at 1339, even though Prime95 is still calculating away. Hmmm?!?

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