Hardware Reference
In-Depth Information
cessors 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 pro-
cessor 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 ad-
equately cool the processor. Because they must account for extreme circumstances, all
modern systems and heatsinks are designed to operate properly if the external environ-
mental 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 environ-
ments with higher temperatures than that, PCs require more specialized designs.
Table
3.26
shows the maximum heatsink air inlet temperatures allowed for various processors
with factory-installed heatsinks.
Table 3.26 Maximum Heatsink Inlet Temperatures for Various Processors
Asyoucansee,foralongtimenewprocessorscontinuallymademoredemandsonsystem
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.
Themostdemandingprocessorstodayrequirethattheinternalchassistemperatureremain
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,
