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

Asset ID:	1-71-1003507.1
Update Date:	2009-12-04
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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GCS>Sun Microsystems>Servers>x64 Servers

PreviouslyPublishedAs
204930

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.

Steps to Follow
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.

Product
Sun Fire E25K Server
Sun Fire E20K Server
Sun Fire 15K Server
Sun Fire 12K Server

Internal Comments
Audited/updated 12/03/09 [email protected], Entry Level SPARC Content Team Member

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

Change History
Date: 2004-07-28
User Name: C149439
Action: Approved
Comment: Added product trademark. Corrected measurement abbreviations. Edited text.
Gail Waldron
Version: 2
Date: 2004-07-27
User Name: C149439
Action: Accept
Comment:
Version: 0

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