physical characteristics. The following table describes the characteristics of the most common
expansion bus types:
Bus Type
Characteristics
Peripheral
Component
Interconnect
(PCI)
PCI was developed to replace the obsolete ISA and VESA bus
standards. PCI:
Is processor independent, meaning the CPU and PCI bus
can process concurrently
Supports plug and play, meaning installed devices are
detected and configured automatically
Most commonly used by devices such as sound cards,
modems, network cards, and storage device controllers
Can run at 33 MHz and transfer data at 133 MB/s or run at
66 MHz and transfer data at 266 MB/s
PCI Extended
(PCI-X)
PCI-X was built on existing the PCI architecture and aimed to
overcome standard PCI bandwidth limitations. PCI-X:
Uses a 64-bit interface to achieve faster data speeds
Operates at 133 MHz, resulting in data rates of 1.06 GB/s
Is typically used by servers for network cards or Fibre
Channel adapters
Is backwards compatible with standard PCI slots (i.e., a
PCI-X card can be installed in a standard PCI slot)
When installed in a standard PCI slot, PCI-X cards are throttled
down to standard PCI speeds.
PCI Express
(PCIe)
PCIe was developed to replace PCI, PCI-X, and AGP. Instead of a
shared bus, each PCIe slot links to a switch that prioritizes and
routes data through a point-to-point dedicated connection and
provides a serial, full-duplex method of transmission. PCIe uses
several different connection types.
PCIe types are defined by the number of transmission lanes
that are used to transfer data. For example, PCIe x1
provides one lane for transmission (x1), while PCIe x16
provides sixteen lanes for transmission. PCIe defines x2,
x4, x8, x16, and x32 connection types.
PCIe data rates depend on the protocol version and number
of transmission lanes:
o
1.0: 250 MB/s (x1); 4 GB/s (x16)
o
2.0: 500 MB/s (x1); 8 GB/s (x16)
o
3.0: 1 GB/s (x1); 16 GB/s (x16)
o
4.0: 2 GB/s (x1); 32 GB/s (x16)
In addition to greatly increased speed, PCIe offers higher
quality service.
PCIe can run alongside legacy PCI technology (i.e., both
PCIe and PCI buses can be in the same system).
PCIe x1 slots are typically used for network cards, USB
cards, and sound cards. PCIe x16 slots are primarily used
for dedicated video cards.
PCIe cards are cross-size compatible, as long as the slot size is the
same or larger than the card size. For example, a PCIe x1 card can
be installed in a PCIe x16 slot, but a PCIe x16 card cannot be
installed in a PCIe x1 slot.
Mini PCI
Small form factor computers (e.g., laptops or Mini-ITX systems)
might include a Mini PCI slot, which has either 100 or 124 pins
and accepts Mini PCI cards. A typical use for a Mini PCI slot is to
add internal cards (such as wireless cards) to laptops.
Legacy buses
Buses that have been replaced by newer types are considered
legacy buses. Legacy buses are rarely used and include the
following:
AGP (accelerated graphics port) was a dedicated bus type
used by dedicated video cards.
AMR (audio/modem riser) was a riser card that attached to
the motherboard and allowed additional cards (called
daughter cards) to be installed.
