PCI Express
PCI Express is a point-to-point architecture and uses a serial data transmission protocol. A single PCI
Express lane consists of four wires and can transmit 250 MB/s in a single direction or 500 MB/s in both
directions simultaneously. This bandwidth is not affected by what is happening on other PCI Express
buses or legacy PCI/PCI-X buses (provided that total bandwidth can be handled by the CPU and the
memory subsystem.) The transmission protocol is somewhat similar to that used for a LAN connection
and contains error correction and detection, packet addressing, and other network features.
PCI Express improves system attributes. PCI Express enables a low-power, scalable, high-bandwidth
communication path with a small number of connections (wires) compared to traditional parallel
interfaces (for example, PCI).
The PCI Express I/O slots can support other PCI Express cards with lesser bus bandwidth than what is
physically defined for the slot. Use the following table to determine compatibility.
For example, a PCI Express x8 card does not work in a PCI Express x1 slot, but a PCI Express x1 card
works in a PCI Express x8 slot.
Table 5-5 PCI Express compatibility matrix for xw9400
Slot 1*
x16 mechanical
x8 electrical
Slot 2
x16 mechanical
x16 electrical
Slot 4
x16 mechanical
x8 electrical
Slot 5
x16 mechanical
x16 electrical
PCI Express
x1 Card
Yes Yes Yes Yes
PCI Express
x4 Card
Yes Yes Yes Yes
PCI Express
x8 Card
Yes Yes Yes Yes
PCI Express
x16 Card
Yes Yes Yes Yes
* Slot 1 is for short cards only.
ENWW Removing and replacing components 81
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