As new PCs run faster and hotter, they require more and larger cooling fans, which can be very noisy. Modern CPUs and operating systems automatically reduce power during inactive times, helping cooling, but they rarely throttle back noisy fans.
Some PCs can control fan speed (check your BIOS for "Smart Fan Control" or "Noise Control"), but if yours doesn't, you can still enjoy some quiet with free software like SpeedFan ( www.almico.com/speedfan.php ).
SpeedFan reads the temperature sensors built into modern CPUs and motherboards, then alters fan speeds, based on the temperatures. However, the program requires three elements to work: Your hardware must support fan-speed changing, the hardware temperature sensors must let software read their values, and you need to configure SpeedFan yourself. You'll want to research safe operating temperatures and get a sense of the temperatures at which your computer runs.
Though slower fan speeds will lead to hotter-running machines, as long as your processor, hard drive, and other equipment stay within the manufacturer's acceptable operating temperature range, your hardware is safe. Safe operating temperatures are around 70*C for processors and 55*C for hard drives. You can determine your Intel CPU's maximum operating temperature on Intel's Web site ( www.intel.com/support/processors/pentium4/sb/CS-007999.htm ). For AMD CPUs, check the "Case Temp" value on the Technical Documents Page ( www.amd.com/us-en/Processors/TechnicalResources ) for your specific CPU. You'll find the maximum temperature of your hard drive on the manufacturer's Web site.
Armed with this info, install and run SpeedFan. It begins in "passive" mode, where it just reads temperatures and fan speeds, then displays the results. If your hardware is compatible, temperatures and fan speeds are usually listed by number or generic label, but you may need to observe these values while using your computer to determine what they correspond to. The temperature that climbs rapidly during 3D games or while running CPU Burn-in ( http://users.bigpond.net.au/cpuburn ) is the processor, while the other should be the internal temperature of your case. HD0 is the hard drive's temperature. Your video card or power supply's temperatures may be listed here as well.
Fan speeds should range between 500 and 5,000 RPM, depending on the fan's capabilities. If your readings go much beyond these values, then your computer can't accurately report fan speeds and you shouldn't go any further. If they gradually increase and decrease with your computer's workload, then the BIOS is controlling their speeds and you should disable this feature.
Next, try altering the values in the speed fields; these change the speeds of the fans. (You may need to watch your fans to see which setting affects which fan.) Zero percent should stop a fan, while 100 percent will run it at full speed. You should notice a dramatic drop in noise as you reduce fan speeds, and temperatures will climb. You want to find a speed that keeps your system well below the maximum safe temperatures, but is quiet when the system is idling. Set SpeedFan to keep fan speeds low at idle (say, 25 percent), but crank up to a set maximum when a certain temperature (CPU, case, hard drive, or any combination) is reached. You should run through SpeedFan's Help file (accessible through F1) step by step.
Here are the basics: Click SpeedFan's Configure button, then the Temperatures tab. Rename each Temp# something descriptive like CPU or Case. Click the Fans tab and rename each Fan# something like CPU Cooler or Case Fan. Then click the Speeds tab, select a fan, enter values for the fan's Minimum and Maximum values, and check Automatically Variated. Repeat these steps for any fan you want to control, and make sure each fan is checked. Finally, click the Temperature tab again and highlight a temperature. Enter the Desired and Warning temperatures, and put a checkmark by each fan that you want "sensing" the temperature changes. Repeat this for all the listed temperatures, click OK, and then check Automatic Fan Speed. Finally, copy the SpeedFan shortcut to your Startup group so it launches when rebooting.
The fans should now spin at low speeds until a temperature reaches the desired setting, at their high speed above it, and at 100 percent after the Warning temperature is reached. If all goes well, you'll be rewarded with a quiet system when it's relatively inactive, but it will stay cool (and loud) when things heat up. It's the best of both worlds.
Warren Ernst is a professional computer consultant. He blogs at http://warrenernst.com.