Datasheet
20
Chapter 1
N
Personal Computer System Components
attached to it (as shown in Figure 1.12). These devices are used to draw away and disperse the
heat a processor generates. This is done because heat is the enemy of microelectronics. Theo-
retically, a Pentium (or higher) processor generates enough heat that without the heat sink it
would permanently damage itself and the motherboard in a matter of hours or even minutes.
FIGURE 1.12 Two heat sinks, one with a fan
Sockets and slots on the motherboard are almost as plentiful and varied as processors.
Sockets are basically flat and have several rows of holes or pins arranged in a square, as
shown in Figure 1.13. The top socket is known as Socket A or Socket 462 and has holes
to receive the pins on the CPU. The bottom socket is known as Socket T or Socket LGA
775 and has spring-loaded pins in the socket and a grid of lands on the CPU. The land
grid array (LGA) is a newer technology that places the delicate pins on the cheaper moth-
erboard, not the more expensive CPU, opposite to the way the aging pin grid array (PGA)
does. The device with the pins has to be replaced if the pins become too damaged to func-
tion. PGA and LGA are mentioned again later in this chapter in the section “Identifying
Purposes and Characteristics of Processors.”
Modern CPU sockets have some sort of mechanism in place that reduces the need to
apply the considerable force to the CPU that was necessary in the early days of personal
computing to install a processor. Given the extra surface area on today’s processors, exces-
sive pressure applied in the wrong manner could damage the CPU packaging, its pins, or
the motherboard itself. For CPUs based on the PGA concept, zero insertion force (ZIF)
sockets are exceedingly popular. ZIF sockets use a plastic or metal lever on one edge to
lock or release the mechanism that secures the CPU’s pins in the socket. The CPU rides on
the mobile top portion of the socket, and the socket’s contacts that mate with the CPU’s
pins are in the fixed bottom portion of the socket. The Socket 462 image in Figure 1.13
shows the ZIF locking mechanism at the edge of the socket along the bottom of the photo.
For processors based on the LGA concept, a socket with a different locking mechanism
is used. Because there are no receptacles in either the motherboard or the CPU, there is
no opportunity for a locking mechanism that holds the component with the pins in place.
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