CompTIA A+ Certification All-in-One Exam Guide

Expansion Bus
Expansion slots have been part of the PC from the very beginning. Way back
then, IBM created the PC with an eye to the future; the original IBM PC had
slots built into the motherboard—called expansion slots—for adding
expansion cards and thus new functions to the PC. The slots and
accompanying wires and support chips on the first PC and on the latest and
greatest PC are called the expansion bus.
Structure and Function of the Expansion Bus
As you’ve learned, every device in the computer—whether soldered to the
motherboard or snapped into a socket—connects to the external data bus and
the address bus. The expansion slots are no exception. They connect to the
rest of the PC through the chipset. Exactly where on the chipset varies
depending on the system. On newer systems, the expansion slots connect to
the CPU (see Figure 6-17) because modern CPUs contain a lot of controller
features that used to be in the chipset. In older systems, the expansion slots
connect directly to the chipset (see Figure 6-18). Finally, many systems have
more than one type of expansion bus, with slots of one type connecting to the
CPU and slots of another type connecting to the chipset (see Figure 6-19).
Figure 6-17 Expansion slots connecting to CPU