http://www.ComputerBob.com/guides/guide_cpu_cooling.php .
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by ComputerBob
January 25, 2003
Last Updated February 2, 2003
As most people know, too much heat can damage a PC's CPU (main brain). A CPU that constantly runs too hot will have a shorter life than one that runs cooler, and could also cause problems like random shutdowns and the loss of important data. Many modern CPUs have a safety feature that will slow them down or shut them off before they can be damaged by heat, but, I've read that if someone forgets to install its heatsink and fan before powering it up, an AMD Athlon XP CPU can overheat "burn up" in only a few seconds. This article details how I was able to significantly reduce my PC's motherboard and CPU temperatures.
When looking for ways to cool a PC's CPU, the first thing to do is
reduce the overall temperature inside the PC's case, because that's
where the CPU "lives." 
The
best way to do that is to create an airflow that brings in cool air
from the lower front of the case and exhausts hot air out the back of
the case. After all, the fan that cools your PC's CPU can't work very
well if it's blowing hot air onto your CPU. Don't make the mistake of
thinking that your power supply's fan will cool your entire PC, like
it did in older PCs. A power supply fan is designed to keep the power
supply cool, not circulate fresh air throughout an entire PC. Add to
that the fact that modern high-speed CPUs, hard drives, graphics cards,
sound cards, and other components generate much more heat than slower,
older components. The result is that modern PCs often need 2 or more
fans in addition to their power supply fan, to draw cool, fresh room
air into the PC and to exhaust hot air out of it. When I built my PC,
its case came with an 80mm exhaust fan mounted in the back. Knowing
that a bigger fan can move more air than a smaller fan running at the
same speed, I moved that 80mm fan to the front of my PC's case to serve
as an intake fan, and I went shopping for a 92mm exhaust fan at a local
computer store. I compared the noise and CFM (cubic feet per minute)
ratings on all of the fan packages. There were quiet fans that didn't
move much air, and there were noisy fans that moved a lot of air. In
the end, I found a combination of noise level and CFM that I could live
with by buying a 92mm Antec "SmartFan." I mounted the 92mm
fan in the back of the case, where the 80mm fan had originally been,
to exhaust the hot air created by my PC's high-speed components. Of
the two types of fans, the exhaust fan is more important than the intake
fan, but if you have an intake fan in the front of your PC and an exhaust
fan in the back of your PC, they work together to increase the flow
of fresh air through your PC's case, which helps all of the components
run cooler.
Another thing that can affect airflow through the case is the type of cables that you use, and their placement in the case. For example, many cases and motherboards come with one or more flat, gray, ribbon data cables that are used to connect floppy drives, hard drives, and CDRW drives. If you use those, try to position them in such a way that they don't block the airflow through your computer. For example, you can try to lay their flat sides up against the outsides of the case. Instead of flat ribbon cables, I bought round data cables that contain all of the same wires as the flat cables, but in a round shape that lets air flow around them more easily. My 450 watt power supply has many power wires, but I moved the ones that I'm not using into the front/upper area of the case, in the unused 5.25" drive bays above my CDRW drive. Now my unused power cables are completely out of my PC's internal airflow.
Once you have established a system for good airflow through the PC's
case, it's time to maximize the cooling of your CPU. I've read that
an AMD Athlon XP processor can be damaged if it ever runs hotter than
70 degrees Celsius (158 degrees Fahrenheit), but most people try to
keep their CPU running much cooler, in the 30-50 degree range (86-122
degrees Fahrenheit). When it comes to 
shopping
for an effective and efficient CPU cooler, there are many cooler manufacturers,
and each one offers several different models, with online prices ranging
from under $5 to about $150 or more (U.S.D). Some coolers are made of
solid aluminum, some are made of solid copper, and others combine a
copper core with aluminum fins. Some are even liquid cooled. Some have
fast, noisy fans, while others have larger, slower, quieter fans. A
few (like mine) have a manual control that lets you change the speed
of the CPU cooling fan to get the right amount of cooling with the least
amount of noise. Each model of CPU cooler is designed for a specific
type of CPU (i.e. AMD Athlon XP) running in a specific range of speeds
(i.e. up to 1700+). Be sure to buy a CPU cooler that is specifically
designed for your specific CPU, or for an even faster version of your
CPU than you have. If you're planning to overclock your CPU (force it
to run at a faster speed than normal), then it's even more important
that you buy a cooler that is capable of dissipating the extra heat
that your overclocked CPU will generate. My CPU is a 2100+ but my CPU
cooler is designed to cool any AMD Athlon XP CPU up to the 2800+ model.
I think it is a very good value, because it cost me only $15 with free
shipping, but it does a great job of cooling (see below). I found ExtremeTech
and Tom's Hardware
and Anandtech
and Overclockers
to be good sources of information on CPU coolers. Those sites are also
good sources of information on all PC components and on building a PC
-- plus, all 4 sites have very helpful and educational online support
forums. The CPU manufacturers themselves (i.e. Intel, AMD, etc.) often
publish a list of CPU coolers that they recommend for their specific
CPUs -- you can't go wrong if you buy a manufacturer-recommended CPU
cooler, unless you're going to overclock your CPU, in which case the
recommended cooler may not be suitable for you. I bought my cooler --
and all the other components to build my PC) from NewEgg.com,
a highly rated
online store that lets you search for coolers by CPU type, manufacturer,
price, etc., and has photos, descriptions, and buyers' comments about
nearly every product it sells. NOTE: If your CPU's warrantee states
that you must use its OEM-included CPU cooler, then you should keep
the OEM cooler, in case you ever need to file a warrantee claim on your
CPU.
I had ordered a Leadtek motherboard to use in my new PC. I had read many complaints about the stock heatsink/fan that comes with AMD Athlon XP CPUs -- mostly that its fan had quit after a few months, and that it didn't do a very good job of cooling the CPU. So, I bought and installed a highly rated CoolerMaster CPU cooler instead of the stock CPU cooler that had come with my CPU. The CoolerMaster's fan and heatsink are each much bigger than the stock CPU cooler's, to help keep the CPU as cool as possible. And the CoolerMaster that I bought has a manual speed control that lets you adjust the speed of the CPU fan to achieve your own desired balance between noise and cooling ability. Between the surface of the CPU and the bottom surface of the heatsink, I used a thin layer of the generic white heat transfer grease, to help transfer the heat from the CPU into the heatsink. Details: Leadtek K7NCR18D-Pro motherboard, generic white silicon heat transfer grease, CPU and RAM running in BIOS-set Turbo mode (overclocked).
When the USB ports turned out to be defective on my Leadtek motherboard, I returned it for a refund and bought an Asus motherboard. I reassembled my PC with the Asus motherboard, using the same CoolerMaster CPU cooler that I had used with the Leadtek motherboard. Because I had read that its high silver content allows it to transfer heat very efficiently, I bought a tube of Arctic Silver heat transfer grease to use instead of generic heat transfer grease, and I polished the CPU-mating surface of the CoolMaster heatsink's copper core with 400 sandpaper. Details: Asus A7N8X motherboard, Arctic Silver heat transfer grease, CPU and RAM running in BIOS-set Aggressive mode (overclocked).
I monitored my CPU and motherboard temperatures for both my Leadtek and Asus setups for two days apiece, using each motherboard's BIOS temperature-monitoring feature, with the CPU at idle (not doing any work). Throughout the monitoring, the following conditions were constant:
| Criteria | Leadtek | Asus | Asus |
|---|---|---|---|
| Ambient room temperature | 19C / 66F | 19C / 66F | 24C / 75F |
| Lowest motherboard temperature | 32C / 89F | 23C / 73F | Not tested |
| Highest motherboard temperature | 34C / 93F | 27C / 80F | Not tested |
| Motherboard temperature after running overnight | 33C / 91F | 23C / 73F | 28C / 82F |
| Lowest CPU temperature | 40C / 104F | 30C / 86F | Not tested |
| Highest CPU temperature | 41C / 106F | 34C / 93F | Not tested |
| CPU temperature after running overnight | 40C / 104F | 30C / 86F | 35C / 95F |
The Asus setup ran significantly cooler than the Leadtek setup, even in a significantly warmer room. Because more than one variable changed between the two setups, I can't attribute the significant temperature differences between them to just one variable. I suspect that each of the following were contributing factors, in various degrees (pun intended):
So, if you're thinking of building your own PC, you'll have fewer problems
if you do your homework and make sure that it's going to run nice and
cool.