Perle Systems Technical Notes
Background on PCI Express®
Perle UltraPort Express Serial Cards
PCI Express® or PCIe™ (formerly known as 3GIO for 3rd Generation
I/O and not to be mistaken with PCI-X) is an implementation of the PCI computer
bus that uses existing PCI programming concepts and communications standards.
PCI Express reflects an industry trend to replace legacy shared parallel buses with high-speed point-to-point serial buses providing a scalable, high-speed, serial I/O bus that maintains backward compatibility with PCI applications and drivers.
PCI Express has the following advantages over PCI:
- Serial technology providing scalable performance.
- High bandwidth—Initially, 5-80 gigabits per second (Gbps) peak theoretical bandwidth, depending on the implementation.
- Point-to-point link dedicated to each device, instead of the PCI shared bus.
- Opportunities for lower latency (or delay) in server architectures than PCI-X.
- Small connectors and, in many cases, easier implementation for system designers.
It has been stated by at least one major server vendor that PCI Express
will replace the PCI, PCI-X, and AGP parallel buses gradually over the next
decade. It will initially replace buses that need the additional performance
or features. For instance, PCI Express will initially be deployed as a replacement
for the AGP8X graphics bus in client systems, providing high bandwidth and
support for multimedia traffic. It will also coexist with and ultimately
replace the PCI-X bus in server systems.
The bandwidth of a PCI Express® link may be linearly scaled by adding signal pairs to form multiple lanes in the following formats: x1, x4, x8, x12 and x16
Each lane is comprised of 4 pins; x1 has one lane, x2 has two lanes, x4 has four lanes, and so forth. Each lane is capable of providing approximately 500MB/s of bandwidth in both directions.
A x1 lane adapter card will operate on x1, x4, x8, x12 and x16 bus connectors at x1 speeds and will not affect performance on the rest of the bus. PCI Express cards will not fit into a PCI or PCI-X card slot ( and vice versa ).
The form factors for PCI Express cards are identical to that of the traditional PCI standard supporting both standard height and low profile sizes.
The PCI Express standard allows for 100% compatibility with
PCI software. Therefore companies can migrate their application to new servers
with the PCI Express bus. Today PCI-X and PCI Express slots coexist in the
same server, however over time only PCI Express slots will be available in
PCI Express slots are now available today on the following servers from major vendors such as ;
- Dell PowerEdge Servers ( 850, 1850, 2800, 6850 )
- IBM eServer xSeries ( X100, X206m, X306m )
- HP Proliant ( ML110G3, ML310G2, ML150G2 )
- Sun Microsystems ( SUNFIRE X2100 )