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What is PCI Express


PCI Express, also named as PCI-E or PCIe (formerly 3GIO, 3rd Generation Input / Output) is the ultimate evolution of conventional PCI bus. Unlike PCI which is parallel,PCI-E is a serial local bus. Intel developed it, and it was introduced on the 915P chipset in year 2004. This new bus tends to connect expansion cards on a motherboard with the aim to eventually replace all the internal bus used to extend a PC, including the PCI and AGP.

How does it work

With PCI Express, serial links are used to connect devices two by two. Each basic serial link operates at 250MB / s and operates at a voltage of 0.8 V with a dedicated power 75W for the whole bus. It also requires less cabling. The term PCI Express line is used in this case. As the tracks used occupy less space on motherboards and connectors being smaller, this reduces manufacturing costs. A significant factor, especially with laptops and high ranges motherboards.

The PCI Express bus can be constructed by combining several lines to achieve a higher output. We can find the PCI Express bus in several versions; there are 1, 2, 4, 8, 12, 16 and 32 lines versions. For example, the transfer rate of PCI Express system with 8 lines (x8) is of 2 GB/s (250 x 8). The PCI Express allows data rates from 250 Mb/s to 8 GB/s in its 1.1 version.

The different PCI buses

  • PCI Express 1x with a capacity of 250MB/s is present in one or two copies on all current motherboards.
  • PCI Express 2x with an output of 500MB / s is less common, reserved for servers.
  • PCI Express 4x with an output of 1000MB/s is also reserved for servers.
  • PCI Express 16x with an output of 4000MB/s is, present on all modern cards is the standard gear for graphics cards.
  • PCI Express 32x with an output of 8000MB/s has the same format as the PCI Express 16x, it is often used on high-end motherboards to power SLI bus or Crossfire configuration. References to these motherboards are often labeled "32". It allows the use of two PCIexpress 16x ports, wired in a 16 lines configuration, unlike conventional SLI, wired in 2 x 8 lines or for basic Crossfire wired in a 1x16 + 1x4 lines configuration. These motherboards are also characterized by the presence of an additional Southbridge solely dedicated to this 32x bus.

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Jean-François Pillou

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