Sun Fire[TM] Servers: Differences Between PCI-X and PCI Express I/O Technologies

Asset ID:	1-71-1003507.1
Update Date:	2011-11-29
Keywords:

Solution Type Technical Instruction Sure

Solution 1003507.1 : Sun Fire[TM] Servers: Differences Between PCI-X and PCI Express I/O Technologies

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Sun Ultra 5 Workstation
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Related Categories


PLA-Support>Sun Systems>Sun_Other>Sun Generic Product>SN-OTH: Gen_Prod
 .Old GCS Categories>Sun Microsystems>Boards>Misc

PreviouslyPublishedAs
204930

Applies to:

Sun Blade 100 Workstation
Sun Blade 1000 Workstation
Sun Blade 150 Workstation
Sun Blade 1500 Workstation
Sun Blade 2000 Workstation
All Platforms

Goal

Description

This document discusses the differences between PCI-X and PCI Express I/O technologies. Sun currently ships PCI and PCI-X based systems and, in the near future, will be shipping PCI Express based systems.

Solution

PCI, PCI-X and PCI Express are industry-standard I/O technologies.

PCI supports 33MHz, 66MHz clock speeds and operates in 64/32bit mode. PCI
supports 5V as well as 3.3 volt signaling.

PCI-X supports 66MHz, 133MHz, 266MHz, and 533MHz clock speeds and is 64-bits
wide. PCI-X 66MHz, 133MHz, 266MHz and 533MHz clock speeds provide the following throughput respectively: 4Gbit/sec, 8Gbit/sec, 17Gbit/sec, 34Gbit/sec. PCI-X cards are backward compatible to the "old regular" PCI-based systems.

PCI-X supports only 3.3 volt signaling. Due to this, PCI-X adapter cards are only backward compatible with previous generation 3.3V PCI systems.

PCI Express is a serial interconnect, point-to-point link, not a parallel multidrop bus as is PCI/PCI-X. PCI Express can run on many lanes: x1,x2, x4,x8, and x16. Each lane gives 250Mbit/sec in single direction and 500Mbit/sec in duplex mode. The x16 lane gives 16Gbyte/sec(128Gbit/sec) throughput. PCI express is similar to Infiniband; they both have serial interconnects and can be used for interconnecting servers and clustering.

PCI-X is a shared bus. For example, all the devices on the bus share a single set of data lines and signal lines. PCI-Express is a switched bus, which should allow much more efficient use of the bandwidth between the devices and the system bus.

Physically, PCI-X and PCI Express are very different. PCI Express requires a different hardware connection, causing old PCI cards not to work in PCI Express slots. But from software perspective or from a driver/writers perspective they are identical, which is what makes PCI Express so attractive. This allows companies to re-use the PCI-X/PCI software for PCI Express.

Internal Comments
Audited/updated 12/03/09 Silvana.Villamil, Entry Level SPARC Content Team Member

PCI, PCI-X, PCI Express
Previously Published As
77128

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