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merlin · 12:14 AM

The Basics of Hardware Cooling

Introduction

This article is intended for someone who has just completed building a computer or who is planning on building one. It will explain all the components of keeping the hardware in a computer reasonably cool, including processor cooling, graphics cooling, and case airflow. Keeping computer hardware cool is extremely important to the health of the hardware, and having a computer with hardware that functions properly largely depends on keeping the hardware within safe temperatures. A processor that is overheating can cause a variety of problems, including random shutdowns, operating system crashes, overall system instability, and more. Video cards have different overheating symptoms that usually don’t include shutdowns, but instead appear as mistakes in video rendering calculations that are shown by artifacting of random pixels and strange glitches on the screen. If these are overlooked, permanent damage to the graphics chipset and video memory can occur. This article for the most part does not apply to laptops, however some aspects such as the use of thermal compound and temperature monitoring utilities are the same.

Part I: Central Processor Cooling

The most common source of heat and heat related problems in computers is the processor or CPU (central processing unit). CPUs have always been considered the “brains” of a computer, and are usually the most powerful and expensive component. CPUs today are manufactured by two companies. Intel is the original manufacturer of processors; they made the 80386 processors, the first x86 processors with a 32-bit architecture, which powered some of the first affordable home computers. They were manufactured and primarily used from the mid 1980’s to early 1990’s. AMD is the other manufacturer; they became a major player in microchip manufacturing with their AMD K5, which was released shortly after the first Intel Pentium in the mid 1990’s.

As mentioned earlier, processors, even the early processors that are now obsolete, produce a large amount of heat. A device called a heatsink is used to control the heat. A heatsink is a piece of metal or heat conductor with fins placed over a heat source with the purpose of increasing the surface area, and increasing heat dissipation as a result. A processor should never be run without a heatsink; doing so will destroy the processor. There are two kinds of heatsinks, passive heatsinks and active heatsinks. Passive heatsinks are just metal fins, while active heatsinks include an attached fan. The proper way to use an active heatsink is to have the fan blow toward the heatsink rather than away from it. Heatsinks are different from heatspreaders such as those found on RAM; heatspreaders usually do not have fins that heatsinks are designed with, but instead are just pieces of metal to draw heat away from the heat source. If a computer case has a side air duct, then this should draw air into the case and onto the heatsink. For water cooled systems, the heatsink is replaced by a water block through which cool water or coolant is pumped in from a reservoir, and hot water is pumped out to a heat exchanger or radiator that is usually located outside the case or mounted several 5.25" drive bays.

CPUs can be purchased in two ways. They can be bought in retail boxes, which include the processor, a heatsink, warranty, and installation instructions. The other type of packages available for sale are OEM (original equipment manufacturer) packages, which include only the processors themselves. Stock heatsinks that come with retail CPUs are almost always sufficient for keeping the processor cool. Most computer technicians will agree that the only modern processor that usually will need a third party heatsink and absolutely must have high density thermal compound (this is explained further in the next paragraph) at stock speeds is the Intel Pentium 4 Prescott. Pentium 4 processors of that generation are some of the hottest processors still commonly found in modern computers. Although getting a retail box might seem like the most logical option, there are many situations where buying an OEM processor would make more sense. OEM processors are less expensive, and are favored by overclockers because they will be voiding the warranty by overclocking and will most likely have to purchase an aftermarket heatsink anyway. Overclockers should buy OEM heatsinks because they will not obtain the benefits of a retail box, and as a result, buying an OEM processor will be more cost effective. The retail box however is recommended for regular computer builders and for builders of computers with the BTX form factor. Retail boxes are also recommended for builders of computers with the BTX form factor. Special retail boxes are available for sale for use on BTX motherboards in BTX cases. There is no difference in the processor, however the heatsink is optimized for the direct airflow that BTX cases have (this is explained further in Part III).

Another element of CPU cooling is using the high density thermal compound just mentioned. Usually, processors come with wax thermal pads; however these are less effective, and should be removed and replaced with thermal compound when some is available. The compound is placed between the heatsink and the processor and assists in the transfer of heat from the processor die or IHS (integrated heat spreader) by filling microscopic cracks on the heatsink and IHS. Only a very little amount of thermal compound is required; a drop the size of a grain of rice is typically placed on the processor die or IHS. For full instructions on applying Arctic Silver thermal compound, click here.

The temperatures of a CPU can be detected by a sensor located on most motherboards next to the CPU socket. Free utilities like SpeedFan and MobileMeter can read the sensor and report the temperatures to the user. Processor temperatures in desktops should not exceed 60° C or 140° F. If temperatures go higher, damage to the processor can occur. If the temperatures are too high and go above a certain temperature programed into the BIOS, then the BIOS will shut down the computer to prevent damage, however just because a computer isn't shutting down doesn't mean it isn't overheating. If temperatures are too high, then steps such as those described in this article should be taken to control temperatures.

Summary of Central Processor Cooling Information:

A processor that needs a heatsink should never be run without one.
The fan on an active heatsink should be set to blow towards the heatsink rather than away from it.
Retail box processors are usually a better option than OEM processors unless the processor will be overclocked.
Builders of BTX form factor computers should buy retail box processors that are designed for BTX cases.
Thermal pads, or preferably high density thermal compound, should always be used.
Processor temperatures should not exceed 60° C or 140° F.
Free utilities are available to monitor temperatures of processors

Part II: Graphics Card Cooling

In recent years, graphics cards have become more and more important, and have received considerable attention as a result. Modern high-end gaming graphics cards can cost as much as high-end processors, and professional workstation graphics cards can cost over twice that. Graphics card chipsets are manufactured by two main manufacturers, NVIDIA and ATI, with several other companies that make IGPs (integrated graphics processors). NVIDIA calls their graphics chipsets GPUs (graphics processing units), and ATI calls their chipsets VPUs (video processing units). Both companies had their rise to power at about the same time. ATI released the first Radeon VPU, the Radeon 7000, to compete with NVIDIA’s second generation of GeForce GPUs, the GeForce2; both had hardware support for Microsoft’s DirectX 7. Both companies do make cards that their own chipsets are placed on, but for the most part both sell their chipsets to third party manufacturers.

New graphics technology has become more advanced, and graphics cards have gotten more powerful to keep up with the advancing technology. The newer and more demanding chipsets and memory now require much larger heatsinks and fans for additional cooling. High-end graphics cards have very large heatsinks and fans, and some even take up two expansion slots because of the size of the heatsink. These cards also consume a lot of power; gaming computers with high-end graphics cards require 700 to 1000 watts of power. And now, to make graphics performance even more powerful, methods of using dual graphics cards are available. NVIDIA has developed a method of connecting two GPUs and using each to render one output called SLI (scalable link interface). ATI uses a different method of linking VPUs it calls Crossfire. Either technology will significantly increase performance, and increase heat output as well.

Almost all graphics cards come with heatsinks. Additional cooling is usually not required on integrated cards and low-end models, but high-end cards often do need additional cooling. The stock heatsinks are sometimes not enough to cool the components adequately, and aftermarket cooling devices called VGA (video graphics array) coolers can be installed to further control heat. VGA coolers are either large heatsinks that are installed to replace the standard heatsink that video cards come with, or water blocks for water cooled heatsinks. In addition to VGA coolers, expansion slot fans can be purchased to help exhaust hot air out the back of the case using a spare expansion slot. In addition, many cases with side air ducts for processors will also have side air ducts or vents for graphics cards to help draw cool air in.

Like processors, video cards have free utilities for monitoring temperatures. For NVIDIA GPUs, a program called RivaTuner can be use to detect a sensor located on the card, and ATI VPUs have a sensor that can be read using a set of utilities called ATI Tray Tools. If a mid-range to high-end video card is installed in a computer, then it is advisable to take the time and download the software to monitor temperatures since video cards exhibit overheating symptoms in a less noticeable way, and damaging a high-end video card can be very costly to replace. The temperatures of most graphics cards should not exceed 70° C or 158° F, however this can vary slightly depending on the chipset, and some can withstand higher temperatures. If the temperatures do go any higher, then the chipset and memory risk sustaining damage.

Summary of Graphics Card Cooling Information:

Modern high-end graphics cards need attention when it comes to cooling.
Graphics cards almost always come with heatsinks, but VGA coolers are sometimes required.
Expansion slot fans can be purchased to help exhaust hot air from graphics cards.
Graphics card temperatures in general should not go above 70° C or 158° F.
Free utilities are available to monitor the temperatures of graphics cards.

Part III: Case Airflow Design

Good processor and graphics cooling alone cannot keep your components at adequate temperatures. Case airflow is a very important factor in cooling. Good case airflow involves having well-positioned fans blowing in certain directions. In ATX computer cases, front fans at the bottom should draw cool air in, while fans located higher up in the back and sometimes on the top should exhaust hot air. Power supplies usually have fans, and these should take air in at the bottom and/or exhaust hot air at the back. Unfortunately, one of the major flaws of the ATX motherboard and case design is the fact that the power supply is directly above the processor in most cases, although many now have the power supply at the bottom. Because power supplies often have fans on the bottom, they will take in hot air from the processor. This is why it is very important to have at least one large fan in the back; having more than one will be better for the processor and power supply. Since the air inside the case will get hotter as hot components release heat energy, the air will rise, and no fan blowing up is necessary. As mentioned earlier, side air ducts should also be intake fans. In general, larger cases such as ATX Full Towers have better airflow than smaller cases such as the common ATX Mid-Tower because there is more room for air to move. BTX cases have a slightly different design. The goal of the BTX form factor is to be able to cool small cases efficiently by having a more direct airflow with fewer obstructions between the intake and exhaust fans, as well as with the processor farther away from the power supply. BTX cases for the most part use power supplies with the same form factor as ATX power supplies, and as a result don't have a change in power supply cooling. BTX motherboards don't have the flaw mentioned earlier that ATX motherboards do; BTX motherboards have the processor in the middle of the motherboard away from the power supply.

Another important but often overlooked factor is the ratio of intake to exhaust fans. There should be more fans exhausting hot air than taking cool air in. This way, vents located near drive bays and other places at the front of the case, as well as over the CPU and video card if no side air duct is present, will draw air in without the need for a fan. To get the maximum efficiency out of fans, use the largest fans possible. 120mm fans will move the most amount of air with the least speed, and therefore the least amount of noise. If fans are too noisy when running at full speed, then fan controllers that fit in a front drive bay can be purchased inexpensively to slow down the speed of the fans when the components are not under load, and as a result not producing as much heat.

Unfortunately, having fans alone won’t get the job done. It is important to make sure that cables and connectors, especially PATA (parallel advanced technology attachment) and floppy cables, do not obstruct airflow. These are called ribbon cables because they have parallel wires that are very wide like ribbons, and as a result, can significantly block the airflow created by the fans. It is recommended that round PATA and floppy cables, which will obstruct airflow less, are purchased to replace the standard ribbon cables that come with motherboards and retail hard drives. Newer hard disks and some optical drives that use the SATA (serial advanced technology attachment) interface have much thinner cables, and are favored not because they are newer and have a higher bandwidth, but because they are thinner and interfere with case airflow a lot less. In addition to cables, dust can obstruct fans. All computers should be dusted out every 2 to 3 months with a can of compressed air that can be purchased inexpensively at most electronics and office supplies stores.

Many computer builders often talk about water cooling and want to implement it in their own computers. Water cooling however is an extreme form of cooling, and is usually not necessary for normal computer users, or even light overclockers. Quality aftermarket heatsinks can cool processors well enough even with moderate to high overclocks. Water cooling is only a necessary step when there is an excessive number of heat producing components present in a medium to small case, such as an ATX mid tower. An example would be a dual processor system with two pairs of high performance RAM, a top-of-the-line chipset, and two high-end graphics cards in SLI or Crossfire. For that example, water cooling would be available for all the high heat producing components. Another situation where water cooling might be necessary would be a computer located in a hot environment. In that situation, the computer would be unable to pull in cool air, and water cooling would help if the water was cooled by a thermoelectric cooler, which would cool the water or coolant below the ambient temperature.

The program called SpeedFan that was mentioned earlier can also monitor, and in some cases control, the speed of fans. This makes it easy to tell if any are malfunctioning or acting abnormally in order to detect and correct the problem. It can also eliminate the need to buy a fan controller.

Summary of Case Airflow Design Information:

Front fans should be intake fans, and rear and top fans should be exhaust fans.
ATX computer cases should have at least one large intake fan and one large exhaust fan.
Power supplies should draw hot air in at the bottom, and exhaust it at the back.
ATX cases with power supply bays at the bottom will have fewer power supply and processor heat problems.
Side air ducts in cases for processors and graphics cards should draw cool air in if present.
BTX cases have a more direct airflow than ATX cases and are usually smaller.
ATX Full Tower cases will have better airflow than smaller cases such as ATX Mid-Towers.
There should be more fans exhausting hot air than taking cool air in.
Larger fans like 120mm fans will be more efficient and will move more air with less speed and noise.
Fan controllers can be purchased to slow down noisy fans when the computer is idle.
Standard ribbon cables should be replaced with round ones, and SATA drives are preferred over PATA drives.
The inside of a computer case should be dusted out with compressed air about every 2 to 3 months.
Water cooling is only needed for computers with small cases and/or in hot environments.
A program is available to monitor and control the speed of noisy fans.

Closing Statement

Taking all the necessary steps for cooling a computer can seem like a large task, but it is not difficult. It is broken down into the three main categories, processor cooling, graphics cooling, and case airflow. If the steps mentioned in this article are implemented when the computer is purchased or built, then overheating components will not be a problem, and the computer will have no heat-related hardware problems that subtract from the life of the components. A well-cooled computer can easily last 8 to 10 years, and sometimes longer than that, despite becoming obsolete.

Merlin...

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