Hardware Reference
In-Depth Information
voltage regulators, disk drives, and other heat-generating components (including the pro-
cessor). Even with all these devices producing heat, the specifications for many newer
processors require that the air temperature inside the chassis at the heatsink rise only to
3°C (5.4°F) over ambient. This places extreme demands on the chassis cooling.
Conventional chassis are incapable of maintaining that low of a differential between the
chassis interior and ambient temperatures. The only way to achieve that has been by
adding an excessive number of fans to the system, which unfortunately adds cost and sig-
nificantly adds to the noise level. 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 areoftenreferred toas
thermally advantaged chassis
.Usingathermally ad-
vantaged 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 re-
main 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 Septem-
ber2003.TheCAGprovidedspecificationsforaprocessorductandforanadditionalvent
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 pro-
cessors and the development of K10 processors from AMD, most of which have thermal
design power specifications of 95W 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).
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
