Buses and Expansion Slots
September 27 (Day); September 19 (Night)
What is an Expansion Bus:
oExpansion buses are special connections on the motherboard that enable you to add
hardware to the computer that didn’t come with it (p. 111).
oBuses carry four types of “cargo”:
Electrical power
Control activity
Memory addresses
Data
oThese expansion devices (sound card, video card, etc.) connect to the expansion
buses at connections called expansion slots.
oExpansion slots allow any compatible type of device and brand of device to work. In
other words, we can install virtually any device without regard to brand name (p.
111).
oExpansion buses are dependent on the clock chip for their speed. In other words, the
same clock chip that controls the speed of the processor also controls the speed of the
expansion buses, and thus the devices plugged into the expansion slots (p. 112).
However, be aware that the speeds of expansion buses are not the same.
An expansion bus connects to the Northbridge before connecting to the
processor.
oThere are different types of expansion buses. Each type of expansion bus has a
different number of wires and run at different speeds (p. 113).
oOne measure of quality for a bus is throughput. Throughput is the same amount of
data transferred or processed within a specified amount of time. Usually expressed
as MB/sec.
There are two factors that apply to throughput. One is data width
(number of bits transferred at a time) and the other is speed (how fast the
data is moving).
Types of Expansion Slots:
o8-bit ISA (p. 121):
ISA = Industry Standard Architecture
Dates back to the early 1980s
