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PCI-X Vs. PCI Express

Parallel PCI standards with 5 V and 3.3 V are incompatible. Whatever is electronically possible is allowed mechanically.

Source: Digi PCI Technology Overview.

When looking at the comparison table below, you might be tempted to question whether PCI-X would be rendered superfluous. While PCI Express will mainly be around in desktop systems, PCI-X will remain the prevailing high-performance interface for high-end workstations and server systems. Finally, PCI-X 1066 will be able to provide up to 8.5 GB/s.

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Standard Bus Width Clock Transfer
PCI 2.3 32 Bit 33 MHz66 MHz 133 MB/s266 MB/s
PCI 64 64 Bit 33 MHz66 MHz 266 MB/s533 MB/s
PCI-X 1.0 64 Bit 66 MHz100 MHz133 MHz 533 MB/s800 MB/s1066 MB/s
PCI-X 2.0 (DDR) 64 Bit 133 MHz 2132 MB/s
PCI-X 2.0 (QDR) 64 Bit 133 MHz 4264 MB/s
PCI Express 1 Lines, 8 Bit 2.5 GHz 512 MB/s
PCI Express 2 Lines, 8 Bit 2.5 GHz 1 GB/s (Duplex)
PCI Express 4 Lines, 8 Bit 2.5 GHz 2 GB/s (Duplex)
PCI Express 8 Lines, 8 Bit 2.5 GHz 4 GB/s (Duplex)
PCI Express 16 Lines, 8 Bit 2.5 GHz 8 GB/s (Duplex)
PCI Express 32 Lanes, 8 Bit 2.5 GHz 16 GB/s (Duplex)
Patrick Schmid
Editor-in-Chief (2005-2006)

Patrick Schmid was the editor-in-chief for Tom's Hardware from 2005 to 2006. He wrote numerous articles on a wide range of hardware topics, including storage, CPUs, and system builds.