Re: CPU temperature VS. system temperature
From: David Maynard (dNOTmayn_at_ev1.net)
Date: 10/04/04
- Next message: Nathan McNulty: "Re: USB ports not recoginized after SP2"
- Previous message: Joe~~tucson Az: "Hidden hard drive"
- In reply to: Opticreep: "CPU temperature VS. system temperature"
- Next in thread: Al Smith: "Re: CPU temperature VS. system temperature"
- Messages sorted by: [ date ] [ thread ]
Date: Mon, 04 Oct 2004 12:47:51 -0500
Opticreep wrote:
> First of all, thanks to everyone (on a previous thread) who suggested
> a few changes on my PC's fans to improve the CPU temperature. I ended
> up redirecting the fans on the side panel from "exhaust" to
> "intake"... and I moved the extra exhaust fan at the back of my PC
> further down, away from the power supply. The idle CPU temperature
> went from 45 degrees all the way down to 37! And the peak temperature
> under heavy load went from 64 degrees to 58 degrees. I was amazed at
> the drastic temperature drop from simply moving the fans around.
>
> But a strange thing happened: My system temperature went from 32, all
> the way up to 42. I had thought that a better air circulation, which
> lowered CPU temperature, would also lower the system temperature.
> Instead, system temperature went up by a full 10 degrees.
The airflow pattern changed. I can't give you a definitive answer without
being able to look at the board and box but consider that with the side fan
blowing inward it's now 'aiding' the CPU heatsink fan: I.E. moving air in
the 'same' direction. Now consider if the resulting CPU heatsink air is now
blowing more directly down onto the motherboard in a particular area that,
before, it was being pulled away from. And what if that area includes the
'system temp' sensor. It'll be blowing it's warmer exhaust air over that
sensor for less efficient cooling than before, of that spot.
There might be an additional/alternate factor. If that sensor is near the
rear exhaust fan port it's now got warm CPU air going over it to then get
OUT the case rather than outside air coming IN that same hole. Same kind of
effect, the altered airflow is putting warmer air over 'that spot'.
On the other hand, it could be the airflow changed in a completely
different manner, where ever that temp sensor is.
>
> I don't get it at all. I find it hard to fathom that the system
> temperature would be five degrees higher than the CPU temperature.
Because 'the CPU' is where 'the heat' (power) is? Yes, and no.
People often confuse heat FLOW [and power] with temperature and just say
'heat' and 'hot', as if interchangeable, for both but they're not the same
thing. Heat flux comes from the power consumed whereas 'temperature' is the
result of heat flowing through a thermal resistance, or vice versa, just as
voltage is the result of current flowing through an electrical resistance,
or vice versa.
So 'temperature' is the result of power consumed and the thermal resistance
involved in dissipating it, not the absolute amount of power, and, as a
result, a 'low power' device can get a heck of a lot hotter than a high
powered one if it isn't dissipating that 'small' amount of power well.
For example, it isn't uncommon for the power regulator FETs to be hot.
Also, consider that folks worry about how well the northbridge is cooled
but it is certainly not consuming nearly as much power as the CPU. It gets
hot because it has a smaller heatsink and the package itself isn't designed
to dissipate as much power. Less power in but the thermal resistance is a
lot higher.
The difference can be quite dramatic. Put 1 watt through a 1/4 watt
resistor and it'll melt the insides, the case, create smoke and all sorts
of disaster, I.E. get *real* dern hot, while a Prescott CPU, with it's
massive heatsink, is quite happy consuming over a hundred times more power.
temperature != power
(or else improving airflow and using better heatsinks wouldn't help)
So, just because the CPU consumes a hefty amount of power doesn't mean he's
necessarily going to be the hot boy on the block.
> I
> would expect it to be the other way around. In fact, I'm worried now
> that the motherboard's temperature sensors are either broken, or
> unreliable. The system temperature reading remains fairly constant
> (+/- 1 degree) even when the Radeon 9800 Pro card and the CPU are
> working full speed. Is 42 degrees too hot for a system temperature
> during idle time?
Your 'system temp' is probably more like 'motherboard near the regulators'
temp or maybe it's 'motherboard near the northbridge' temp.
>
> Anyway, am I better off with the new setting (CPU 37-58 degrees,
> system 42 degrees) or the old setting (CPU 45-64 degrees, system 32
> degrees)?
Well, I'd go for the lower CPU temp but I'd also want to look around and
find out just exactly where and what that 'system temp' really is.
- Next message: Nathan McNulty: "Re: USB ports not recoginized after SP2"
- Previous message: Joe~~tucson Az: "Hidden hard drive"
- In reply to: Opticreep: "CPU temperature VS. system temperature"
- Next in thread: Al Smith: "Re: CPU temperature VS. system temperature"
- Messages sorted by: [ date ] [ thread ]
Relevant Pages
|
