Chapter 3: Microprocessors^53
Beginning with the 486, processors were cooled with aheat sinkorprocessor cooling
fan(see Figure 3-7) or both, attached directly to the surface of the processor. In addition,
the system fan was reversed to extract the heated air from inside the computer case and
force it out.
The Pentium processor is meant to operate at 185 degrees Fahrenheit (85 degrees
Celsius). The Pentium III processor should operate at 100 degrees Celsius (about 212°
Fahrenheit), which is pretty hot. It is very important that a processor’s cooling system is
kept at or near its designed operating temperature. At too-high operating temperatures,
processors begin to perform poorly, shut down, or become permanently damaged.Heat
sinks, like the one shown in Figure 3-8, and fans (see Figure 3-7) are designed to draw
the heat up and out of the processor’s packaging and carry it away on the tines of the
heat sink and the airflow of the fan.
On the 486, Pentium, and Pentium Pro processors, heat sinks and fans are either
clipped to the processor or attached with a dielectric gel, also calledthermalgreaseor both.
Later Pentium models, including the Celeron, the Pentium II, and the Pentium III, all of
which use SECC (single-edge contact cartridge) packaging, include mounting points for
fans and heat sinks as part of their design.
Commonly, the processor is not the only high-heat device inside the computer case.
Other high-performance devices, such as accelerated video cards and high-speed hard
disk drives, can also produce significant heat. Computer case designs should provide for
enough ventilation to allow cool air to be drawn in and hot air to be expelled. Otherwise,
the computer’s lifespan will be dramatically shorter.
Figure 3-7. A cooling fan for a Pentium III microprocessor