Hardware Reference
In-Depth Information
Many systems with multiple fans on the front, rear, and sides are still incapable of maintaining only
3°C (5.4°F) over ambient at the processor heatsink.
Both Intel and AMD have been releasing documents describing the thermal attributes of their
processors and guides showing ideas for cooling systems and chassis designs that can adequately
cool the system. Chassis that have been specifically designed to improve cooling for the processor by
maintaining a temperature of 40°C or less at the processor heatsink inlet are often referred to as
thermally advantaged chassis
. Using a thermally advantaged chassis allows the processor to remain
cool, even under extreme environmental conditions, and it reduces noise. Most modern processors
and chassis incorporate cooling systems that can adjust the speeds of the fans. If the temperatures
remain below specific limits, the fans run at lower speeds, thus reducing the noise level. If
temperatures rise, so do fan speeds and noise. In general, thermally advantaged chassis enable fan
speeds to remain lower, resulting in quieter operation.
The original specification for a thermally advantaged chassis was known as the Chassis Air Guide
design guide (CAG), originally published in May 2002 and revised in September 2003. The CAG
provided specifications for a processor duct and for an additional vent in the side cover for adapter
cards such as graphics boards. The CAG was developed at a time when the dominant processors in
the marketplace, the Intel Pentium 4 family, had thermal design power specifications as high as
140W.
Since the replacement of the Pentium 4 by cooler-running Core 2 and Core i-series processors and the
development of Bulldozer and Piledriver processors from AMD, most of which have thermal design
power specifications of 125W or less, the requirements for a thermally advantaged chassis have
changed. The CAG design guide has now been replaced by the Thermally Advantaged Chassis (TAC)
design guide (numbered version 2.0 to reflect its origin as an update of the CAG).
Note
If you are building a small form factor PC, such as for a home theater or server, see the
Thermally Advantaged Small Chassis (TASC) Design Guide, version 1.0, available at the
Formfactors.org
website.
To meet the TAC Design Guide version 2.0 requirements (available from the System Design section
of
www.formfactors.org
)
, the following specifications are recommended:
• Accepts an industry-standard ATX, MicroATX, or FlexATX motherboard
• Accepts an industry-standard ATX, SFX, or TFX power supply with integral exhaust fan
• Uses a processor with an active heat sink designed for the processor
• Uses a side cover with an optimized side vent of 100mm wide by 150mm tall. The
recommended open area should be at least 60%.
• Provides a primary chassis rear exhaust fan of 92mm or larger.
Note
One of the major recommendations of the original Chassis Air Guide (CAG) Design Guide
was the use of a processor duct to deliver air directly to the processor heatsink. Although this
was an effective solution to processor cooling, a motherboard upgrade with a different location
