Expansion Bus Types
Expansion slots provide a connection for a number of devices and functions, some internally on
the motherboard and a couple externally. The following table lists common expansion buses in a
PC system:
Slot
Characteristics
ISA is a 16-bit I/O bus slot (a second short slot for additional 8-bits) that
includes DIP switches and jumpers. ISA slots can be found on machines
Industry Standard
ranging from 286 models through Pentium models. ISA buses were used to
Architecture (ISA)
connect peripheral cards to the motherboard, but have been replaced by a newer
bus called EISA (Extended ISA), which has a 32-bit bus.
Supports a 32 or 64-bit I/O bus providing compatibility with both 486 and
Pentium machines.
•
Peripheral
Component
Interconnect (PCI)
•
•
•
Mini-PCI
This bus is processor independent (the CPU and the PCI bus can
process concurrently).
The PCI bus can support ISA and EISA (if PCI and ISA share a bus,
then the use of one disables the other).
PCI is plug-and-play.
PCI buses are most commonly used for devices such as sound cards,
modems, and network cards.
Small form factor computers, such as laptops or micro-ATX systems, might
include a mini-PCI slot. Mini-PCI devices are small cards with either 100or 124-pins. A typical use for a mini-PCI slot is to add internal cards (such
as wireless cards) to laptops.
PCI Express (PCIe) is a next generation I/O bus architecture. Rather than a
shared bus, each PCIe slot links to a switch which prioritizes and routes data
through a point-to-point dedicated connection and provides a serial fullduplex method of transmission.
Peripheral
Component
Interconnect
Express (PCIe)
•
•
•
•
Accelerated
Graphics Port
Basic PCIe provides one lane for transmission (x1), at a transfer rate
of 2.5 Gbps. It can also provide multiple transmission lanes (x2, x4,
x8, x16, x32).
In addition to greatly increased speed, PCIe offers higher quality
service.
PCIe is backwards compatible and allows legacy PCI technology to
be run in the same system.
PCIe buses are most commonly used for video cards in modern
computer systems.
Similar to PCI, but designed specifically for graphics support. Motherboards
that provide AGP support have a single AGP slot. AGP is commonly used
(AGP)
for video cards in modern computer systems, but is being replaced by PCIe.