Installing the CPU Cooler
Today's fast processors generate a tremendous amount of heat. Without a good CPU cooler, a modern processor would burn out in mere seconds. That's one of the reasons that this revision of the site includes a page dedicated to keeping your homebuilt computer cool. If you haven't read it already, I suggest that you read it now.
Inadequate cooling also can result in data errors, performance problems, and reduced processor life. CPU manufacturers typically provide lists of "approved" coolers for their chips. These coolers may or may not be any better than other coolers, but using a non-approved cooler might void the CPU's warranty.
To extend your homebuilt computer's life and maximize its performance while not running the risk of voiding the CPU warranty, I recommend that you use the best cooler you can find that has been manufacturer-approved for your particular processor. The processor cooler is not a place to skimp. It would be a shame to spend all that time and money to build your own computer, and then the CPU burns up because of an inadequate or poorly-designed cooling fan.
Parts of a CPU Cooler
Fan-and-heatsink CPU coolers are composed of three parts: a fan, a heat sink, and a mounting device that attaches the cooler assembly to the motherboard directly over the processor.
Liquid CPU cooling systems consists of a CPU block (or "water block") that attaches to the CPU, a pump, a radiator, and hoses to hook them together. Sometimes these parts are combined into an "AIO" or "all-in-one" liquid cooling system.
In addition to the cooler itself, another important element of the cooling system is something called "heat sink compound," "thermal paste," or "thermal jelly." It's applied between the heatsink and the die of the processor to improve heat transfer from the processor to the heatsink, which in turns improved cooling.
Many heat sinks come with a patch of heat sink compound pre-applied to the heat sink itself. The actual compound is covered with a little plastic tab during shipping. The heat sink compound pre-applied to a high-quality heat sink is usually adequate for ordinary use, but not necessarily for overclocking or prolonged hard use.
If you are using a heat sink with pre-applied heat sink compound, then all you need to do is peel the protective tab off the heat sink prior to installing the cooler. It's very simple. Forgetting this simple step, however, can cause serious damage to your processor.
If your heat sink doesn't have pre-applied compound (or if you don't want to use the pre-applied compound), you will need to remove the pre-applied compound and apply the paste you want to use directly to the processor die.
Make sure to completely remove the existing compound, preferably using alcohol prep pads. You can also use 91 percent (or higher) isopropyl alcohol; but remember that 91 percent alcohol is 9 percent water, so be careful not to drip it.
You'll also need to remove and replace the thermal paste if, for some reason, you have removed and are replacing the heat sink. You have to gently remove the old paste from both the processor and the heat sink and replace it with new paste before replacing the cooler.
Thermal paste doesn't exactly go bad, but it does dry out over time. If after several years you notice your CPU temperature starting to creep up to temperatures that affect the computer's performance or endanger the processor, dried-out thermal paste is one possible cause.
When it's necessary to remove old heat sink compound, do it gently. Wipe the jelly off the processor and the heat sink with a clean, lint-free cloth or paper towel. If there are a few stubborn spots, use a fingernail or a wooden tongue toothpick to scrape it off. Then finish up with an alcohol pad or a swab moistened with a bit of alcohol.
I suggest you use a high-quality thermal paste like Noctua NT-H2 or Arctic MX-5, or a silver-based thermal jelly like Arctic Silver. The difference in price between the good stuff and the cheap stuff is trivial, and high-quality thermal jelly will help keep your processor cool and comfy.
Be careful not to get any heat sink compound on the motherboard! Most heat sink compounds contain metals and are conductive. They can short out the circuitry on the motherboard if they get on the traces. (Thanks for pointing out that omission to me, Bob.)
Mounting the CPU Cooler
Once you've applied the thermal paste, the CPU cooler assembly is positioned over the processor and secured to the motherboard.
Some motherboards use metal clips to hold the cooler down, some use plastic clips, and some have to be screwed down.
Aftermarket air coolers usually come with special backing plates and almost always have to be screwed down.
Other coolers have plastic pins that you push into the motherboard with your fingers. No tools are required. Once they're in, they hold very well and can, in fact, be very hard to remove.
Notice that on older bail-type sockets, both the socket and the heat sink are offset from center a little to accommodate the bail. Make sure you install the cooler with its offset on the same side as the offset on the socket.
In this picture, my brother had to use a slotted screwdriver to gently, but firmly, hook the retaining clips under the tabs on the processor socket, being very careful not to let the screwdriver slip. If it had scratched the surface of the motherboard, the mobo could have been ruined.
Installing a liquid CPU cooler is pretty similar except that instead of mounting a fan on the processor, you'll be installing a CPU block (or "water block") on the processor. The CPU block in turn is connected with hoses to a pump and a radiator or to an all-in-one CPU cooler. The radiator (and fan, if any) usually are mounted in one of the fan openings in the case.
Liquid CPU cooling systems maintain more consistent control of CPU temperatures across all processor load conditions, but especially during sustained, CPU-intensive use such as gaming or video encoding. They're also considered a necessity by most computer hobbyists who overclock, and are much quieter than fan-and-heatsink coolers running at full speed.
Powering the Cooling System
If you're using air cooling, simply plug the fan leads into the appropriate motherboard headers.
DC fans plug into three-pin connectors on the motherboard that are (appropriately enough) labeled "CPU Fan" in teensy-weensy letters. Their speed is controlled by varying the voltage to the fans
PWM (Pulse-Width Modulation) fans use four-pin connectors that allow the system to both sense and control the fan's speed based on cooling needs. The voltage is always 12 volts in a PWM system. The speed is controlled by varying the width of the control pulse.
If you want, you can "hotwire" the fan using an adaptor that directly connects it to the power supply, which causes it to spin at full speed all the time. I strongly recommend you not do that. It creates a lot of noise, uses more power, and causes the fan to wear out sooner.
Some people also believe you can "over cool" the CPU by running the fan at full speed all the time. I personally don't think that's possible unless you're using the computer outdoors at the North Pole, but some people disagree.
In most cases, you also can disable the fan speed control in CMOS setup. That has the same effect as hotwiring the fan, and I don't recommend it. The automatic settings are fine for most users. Overclockers can use software from the motherboard manufacturer (or sometimes built into BIOS) to create custom fan curves to suit their needs.
If you want a little extra cooling without creating a custom fan curve, check your motherboard manual to see if there is an option in BIOS to increase the fan speed. Many have settings for "high performance," "gaming," or some other setting that will increase the fan speed across the processor's operating temperature range.
Chipset Coolers
Most modern motherboards also have a chipset cooler, at least on the Northbridge chipset. These are almost always factory-installed and are adequate for all but the most intensive use. Just blow the fan out with canned air once in a while. You only need to replace it if it stops spinning or starts making noises, which doesn't happen very often.
If you do find it necessary to replace or upgrade the factory-installed chipset cooler, the process is basically the same as installing a CPU cooler. The main difference is that chipset coolers usually are fastened to the motherboard using spring fasteners or plastic retainers rather than a metal clip.
You may need to have access to the back of the motherboard to remove the fasteners, and you may have to install new fasteners if the old ones can't be removed without breaking them.
Now that we've installed the cooler, let's move on to the next step: Installing RAM.
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