PCI
Express is positioned as the industry's third-generation I/O
technology. First generation was ISA, second generation being PCI, and
the third generation, PCI Express. PCI Express is designed to be a
general-purpose serial I/O interconnects that can be used in multiple
market segments, including desktop, mobile, server, storage and
embedded communications. PCI Express can be used as a peripheral device
interconnects, a chip-to-chip interconnects, and a bridge to other
interconnects like 1394b, USB2.0, and Ethernet. It can also be used in
graphics chipsets for increased graphics bandwidth. PCI Express is an
implementation of the PCI computer bus that uses existing PCI
programming concepts and communications standards, but bases it on a
much faster serial communications system. PCI Express is intended to be
used as a local bus only. The PCI Express multi-drop, parallel bus
topology provides Host Bridge and several endpoints. This introduces a
new element, the switch into the system which replaces the multi drop
bus and is used to provide fan-out for the I/O bus. A PCI Express
switch provides high performance I/O and can coexist in many platforms
to support today’s lower bandwidth applications until a compelling
need, such as a new form factor, causes a fully PCI Express platform.
Due to it being based on the existing PCI system, cards and systems can
be converted to PCI Express by changing the physical layer only -
existing systems could be re-booted on PCI Express and never even know
it. The higher speeds on PCI Express allow it to replace almost all
existing internal buses, including AGP and PCI.
