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Topic Title: Guide to System Thermals
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Created On: 03/28/2004 02:31 AM
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 03/28/2004 02:31 AM
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It is a common question to ask "What temperature should my processor be running at?"

However, this is not a valid question. What might be an average or normal temperature on one system may not be normal on another system. This is because the thermals of of any given system are dependent in large part on the system configuration. There are several high heat generating devices in modern systems. Video cards, processors, chipsets, hard drives, DVD drives, high speed CDRom drives all generate a great deal of heat. Properly dissipating the heat build up inside the case is essential to maintaining a stable system. To to this, there are several components that must be considered for proper cooling.

The primary purpose of any heatsink is to draw heat away from the heat generating device. Heatsinks can be found on several components inside a computer system. Processors, video cards and chipsets are the main components that use heatsinks. Heatsinks work because they use highly thermally conductive materials such as aluminum, copper, nickle, etc. and create a large surface area. Heat will always travel from the source and radiate out towards the cooler areas, this is why large surface areas are an important part of the heatsink design. Heatsinks are a passive form of cooling since they have no moving parts nor require any power.

However, passive cooling is rarely enough to properly cool a modern system. Often times, heatsinks are used in conjunction with fans. The addition of a fan makes the heatsink/fan (HSF) combination an Active Cooling solution. The effectiveness of a fan is often measured in CFMs (Cubic Feet per Minute). This determines how much air a fan is capable of moving in a given period. Higher CFM's means more air flow across the heatsink and therefore better cooling. However, the higher the CFM, the more noise generated. The amount of CFM's a fan is capable of moving is determined in large part by the speed of the rotation (in RPMs), the number and surface area of the fan blades, the size of the fan, and the pitch (or angle) of the blades.

Since most video cards and chipsets will already have the HSF installed, it is not necessary to worry about selecting the proper solution for these devices. The manufacturer will have already taken care of that aspect during design of the component. However, it might be necessary to select a HSF for the processor. Great care should be taken to select the right HSF for the processor. Refer to the manufactures website or contact them directly for a list of recommended solutions.

Note: This guide does not cover any aspects of water cooling or other active solutions since that is a in depth topic that deserves its own guide.

Thermal Interface Materials
Thermal Interface Material (TIM) is a highly thermally conductive material that helps transfer heat from one device (typically source device) to another (typically HSF). Whenver 2 surfaces come in contact, there are microscopic air bubbles between the surfaces. Air is a poor thermal conductor, therefore filling these bubbles with a high thermally conductive material will help improve the efficiency of the overall solution. There are many types of thermal materials from Phase Change Material (PCM) to thermal tape to thermal grease. Thermal tape is rarely recommended as it is typically not suited for processor applications. PCM or grease are the more common materials used on modern processors. Each solution has is advantages and disadvantages. Greases are often more thermally conductive, but tend to be more difficult to work with and create more mess. Many greases are also electrically conductive or capacitive and can short out the processor if it comes in contact with any surface mounted components on the processor package. PCM is usually pre installed but is only good for a one time use. Once the heatsink is removed after processor has been powered on, the material needs to be replaced.

Since PCM is usually preinstalled on the heatsink there is no need to worry about using the proper amount. If a replacement PCM pad is required, it will usually come in a 1x1 inch square pad, so again, the amount is already resolved. However, the old pad should be completely removed from the heatsink before applying the new pad.

When working with thermal greases (or pastes), care should be taken not to use too much. Some people think that if a little is good, then a lot should be great. THIS IS THE WRONG APPROACH. Too much thermal grease will act as a blanket, trapping heat inside the processor. The amount of grease to use should be no more than the size of a grain of rice. It should be spread evenly over the center of the heatsink. Again, care should be taken not to get it all over the processor package. The processor could short out if the grease is electrically conductive or capacitive and it gets onto the proessor bridges or passive components on the processor package. Likewise, the grease should never come in contact with the processor pins.

Note: PCM is not recommended for Athlon 64 or Athlon 64 FX systems due to the strong adhesion created between the processor and heatsink.

Case size is another important component that plays a significant role in the thermal properties of any system. In addition to providing room for expansion components, large cases, typically allow for better cooling since more air is circulating throught the case. A good case should allow for both intake and exhaust fans to be installed in the system. However, large cases take up more space on or under your desktop. There are several form factors to choose from when selecting a case, however, most cases will typically support ATX, uATX (micro ATX) and mini ATX type motherboards. However, smaller cases may not support ATX boards since they are larger than the uATX or mini ATX standards.

As mentioned earlier, the number and type of components in your system will also play a role in the thermal properties. The more components installed, the more heat that will be generated inside the system. This will drive up the ambient temperature inside the case. The higher the ambient temp, the more difficult it will be for HSFs to do their jobs.

Air Flow
In a typical desktop tower form factor, air should flow in from the bottom front of the case and exhaust out the top rear of the case. Ambient air temperatures inside the case will play a large role in the effectiveness of individual solutions used for the processor, video card and chipset. Therefore, expelling excess heat is essential for proper cooling and stability.

As mentioned, a good case will usually allow for 1-2 intake fans (case fans) and 1-2 exhaust fans to assist with air circulation for proper cooling. In some high end cases, there could also be places to install fans on the side case panel as well as in the top of the case. Keep in mind, the more fans installed the better the cooling, but the more noise generated. The goal should be to create negative air flow. This means have more air leaving the case than coming in. Typically, this is done by having more exhaust fans than intake fans. If a case has 2 intake fans at the front, and 2 exhaust fans in the rear, then negative air flow is achieved because the powersupply also has 1 exhaust fan.

Generally speaking expansion slot fans are not a good idea because they will exhaust the cool air straight out the back of the case.

There may be a rare occasion when a expansion slot fan may be needed, but it is usually not recommended.

Singularity2006 has developed a detailed look at System Air Flow.' ">

Tips for Reducing Heat buildup
If a system is running hot, there are a few tips on how to cool it down.

Make sure system is using a high quality heatsink/fan.

Avoid Hot Spots by spacing out high heat generating decvices or cards.

Make sure processor voltage is correct. Many overheat conditions can be traced back to incorrect voltage settings.

Install case fans (if not already installed in case)

Use high quality TIM.

Keep airflow clean by using rounded cables or tie off cables so airflow is not restricted.

Do not block intake vents/fans or place case inside cabinets

Blow out dust from inside case on a routine basis. In addition to being charged particles, dust can act like a blanket on top of your components, trapping heat inside.

This list is not all inclusive, but will often help in many overheat conditions. So as you can see, it really makes no sense to ask about normal or average operating temperatures. However, you could ask what temperatures should a system operate at error free? To answer this, PCY has a good write up on error free temps here.' ">

Hope this helps. If you find any of this information incorrect or think I have missed anything, please feel free to PM me.

There are 10 types of people in the world, those that understand binary and those that don't.

The opinions expressed above do not represent those of Advanced Micro Devices or any of their affiliates.

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