Hardware Reference
In-Depth Information
metal clips to plastic fasteners for its latest designs. When installing or removing a heatsink that is
clipped on, be sure you don't scrape the surface of the motherboard.
Heatsinks are rated for their cooling performances. Typically, the ratings are expressed as a
resistance to heat transfer in degrees centigrade per watt (°C/W), where lower is better. Note that the
resistance varies according to the airflow across the heatsink.
Active Heatsinks
To ensure a constant flow of air and more consistent performance, most heatsinks incorporate fans so
they don't have to rely on the airflow within the system. Heatsinks with fans are referred to as
active
heatsinks (see
Figure 3.51
). Active heatsinks have a power connection. Older ones often used a spare
disk drive power connector, but most recent heatsinks plug into dedicated heatsink power connections
common to most motherboards. The Socket 478 design uses two cams to engage the heatsink clips and
place the system under tension. The force generated is 75 lbs., which produces a noticeable bow in
the motherboard underneath the processor. This bow is normal, and the motherboard is designed to
accommodate it. The high degree of force is necessary to prevent the heavier heatsinks from pulling
up on the processor during movement or shipment of the system, and it ensures a good bond for the
thermal interface material (thermal grease).
