Hardware Reference
In-Depth Information
Unfortunately, with high-performance processors reaching and even exceeding the 100W power
level, it has become impossible for a standard chassis design to cool the system without resorting to
adding more fans or using more exotic (and expensive) liquid cooling setups. A minor breakthrough
in chassis design has occurred that can allow even processors consuming more than 100W to be
adequately cooled in a three-fan system, without employing exotic solutions or even adding fans.
As you know from the formula earlier in this chapter, processor power consumption is proportional
to speed and is proportional to the square of the voltage it consumes. Even though processor voltages
have been decreasing, speeds have been increasing at a much more rapid pace, such that power
consumption is reaching all-time high levels beyond 120W. To combat this heat, heatsink
manufacturers have increased the efficiency of processor heatsinks significantly over the past 10-15
years. Heatsinks are available today with thermal resistances on the order of 0.33°C/W or less.
Unfortunately, conventional air-cooled heatsinks are fast approaching the limits of the technology.
Improving Thermal Performance
One cost-effective method of improving heatsink performance is to reduce the ambient temperature
around the processor, which means lowering the temperature of air entering the heatsink. To ensure
proper cooling for their boxed (retail) processors, Intel and AMD specify maximum temperature
limits for the air that enters the heatsink fan assembly. If the air temperature entering the heatsink goes
over that amount, the heatsink cannot adequately cool the processor. Because they must account for
extreme circumstances, all modern systems and heatsinks are designed to operate properly if the
external environmental ambient temperature in the room is 35°C (95°F). This means that, in general,
PCs are designed to work in environments of up to that temperature. To operate in environments with
higher temperatures than that, PCs require more specialized designs.
Table 3.29
shows the maximum
heatsink air inlet temperatures allowed for various processors with factory-installed heatsinks.
Table 3.29. Maximum Heatsink Inlet Temperatures for Various Processors
As you can see, for a long time new processors continually made more demands on system cooling.
With the recent trend on the part of Intel and AMD to increase speed through chip design rather than
pure clock speed increases, this trend has plateaued to an extent. The most demanding processors
today require that the internal chassis temperature remain at or below 40°C (104°F), even if the
system is running in a room temperature of 35°C (95°F). The internal temperature rise, or preheating
of air inside the system, is typically caused by heat from components such as motherboard chipsets,
graphics cards, memory, voltage regulators, disk drives, and other heat-generating components
(including the processor). 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 significantly adds to the noise level.
