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PCI Express

A high-speed peripheral interconnect from Intel introduced in 2002. Note that although sometimes abbreviated "PCX," PCI Express is not the same as "PCI-X" (see PCI-SIG and PCI-X for comparison)....

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Definition: PCI Express

A high-speed peripheral interconnect from Intel introduced in 2002. Note that although sometimes abbreviated "PCX," PCI Express is not the same as "PCI-X" (see PCI-SIG and PCI-X for comparison). As a result of the confusion, "PCIe" is the official abbreviation.

Initially used for high-speed display adapters, and intending to eventually replace the PCI and AGP buses entirely, PCI Express was designed to match the higher speeds of today's CPUs. It can accommodate Gigabit and 10 Gigabit Ethernet and even support chip-to-chip transfers.

Switched Architecture
Rather than the shared bus structure of PCI, PCI Express provides a switched architecture using serial communications channels that provide 2, 4 and 8 gigabits per second of interconnect bandwidth in each direction (PCIe 1.0, 2.0 and 3.0). Cards and motherboards are forward and backward compatible between versions.

The channels can be combined in x2, x4, x8, x16 and x32 configurations, creating a parallel interface of independently controlled "lanes." The switch backplane bandwidth determines the total capacity.

Internal in 2002, External in 2007
PCI Express was initially designed for internal connections; however, enhancements extended it outside the box for several meters. For example, External PCI Express allows a laptop to hook up to an external display adapter and monitor, providing greater performance than the laptop's motherboard circuit.

Different Slots
Originally called "Third Generation I/O" (3GIO), PCI Express is software compatible with PCI, but not plug compatible. It also uses slots of different lengths because of the combined lanes (see below). For a comparison of all PCI technologies, see PCI-SIG. See ExpressCard, PCI-X and Thunderbolt.


PCI Express

PCI Express Slot
PCI Express slots are both shorter and longer than PCI and AGP. The x1 slot is a single-lane implementation, while the x16 slot combines 16 lanes for peripherals such as the display adapter.



PCI Express

PCI-Express Vs. AGP
This display adapter from NVIDIA was one of the first x16 PCI Express cards on the market. PCI Express, AGP and PCI cards all have different edge connectors to ensure that they fit into the appropriate slots. (Image courtesy of NVIDIA Corporation.)





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