About cooling...
The safety limit for AMD processors is 85c... you want a heatsink that can keep you as far below that limit as possible.
For a heatsink the CFM of the fan is not the imporatant spec. The best specification to look for is "Thermal Resistence" which is a measure of how much heat the heatsink/fan combination can handle. This is generally stated in "Degrees per watt", indicating how much the temperature of the heatsink (and thus the CPU) will rise for every watt of thermal energy. Obviously this needs to be a very small number, in fractions of a degree per watt to keep a furnace like the AMD CPU cool.
The real math is complex, but this will give you a working approximation:
<b>T == (P x TR) + A</b>
T = approx CPU temperature.
P = cpu power dissipation in watts.
TR = the thermal resistence of your heat sink.
A = ambient temperature (inside the case)
For example... 50 watt cPU, Heatsink TR = .5, Ambient = 25
T == (50 x .5) + 25 == 25 + 25 == 50c. <i>approximately</i>
In practice the final temperature is usually somewhat lower than this approximation indicates... which is a good thing.
The construction of the heatsink also has a bearing on it's eficiency. Believe it or not there is a good reason most look like little aluminum boxes with the fans sitting on top... that's what works.
On a CPU with a built in heat spreader, you really only need an aluminum heatsink to draw heat off the spreader and radiate it out into the air. Copper heatsinks are getting popular but, while they do absorbe heat better, it is far more difficult to get that heat back out and into the air. Plus copper is heavier than aluminum, more than twice as heavy, which puts extra strain on the mouting points. But, this suggests an excellent work around... Hybrids... AMD cpus do not include heat spreaders, like <i>everyone else's</i> cpus do... therefore you've got to find some way of replacing it. This is done by a hybrid construction, a copper slug in the bottom of an aluminum heatsink. The copper draws heat off the cpu and the aluminum cools the copper... It's a very successful combination.
The fan does play a part. Thermal Resistence is usually specified with the fan running at full speed. Reduce the speed of the fan more than a little bit and the TR starts climbing... so rather than worrying about the amount of air moved, you need to look at the heatsink and fan as a system, giving you a specific thermal resistence.
So, what am I suggesting?
For Athlon XP processors you need a hybrid heatsink with thermal resistence below .6
Here's an example:
<A HREF="http://www.spirecooler.com/asp/fcc.asp?ProdID=95" target="_new">http://www.spirecooler.com/asp/fcc.asp?ProdID=95</A>
This is a good cooler, I've used them, but I provide the picture mostly as an example... there are lots of others like it and better.
As for the case cooling question...
This isn't really about CFMs as much as it is about airflow management...
You want to draw cool air into the front of the case, circulate it through as much of the case as you can and then send the warm stuff out the back.
To do this, the intake area of the case must be sufficient that your exhaust fans (in the back) can draw air feely into the case; you need at least as much intake area as you have for exhaust. Too many exhaust fans and all you do is create a vaccuum in the case. Too many intake fans and you create pressure... neither of which is the result of good airflow. In extreme cases, all you end up doing is blowing the hot air around inside the case. The goal is always to move cool air in the front, circulate it through the case, let it pick up heat and the draw it out the back.
Taking a common sense approach, pays bigger benefits than high CFM fans or multiple fans. With good air intakes, on the average computer one standard 80mm, 2700 rpm exhaust fan will provide adequate cooling if you handle it right. (FWIW... that's about 25cfm of airflow)
Hope this helps....
--->It ain't better if it don't work<---
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