What is PCI Express?

PCI Express stands for Peripheral Component Interconnect Express (PCI-E). PCI Express is a new computer format for motherboards allowing for expansion. It was introduced to phase out PCI expansion and the AGP graphics interface card. PCI Express makes a computer work much faster and largely improves the graphics performance of the machine.

Traditional PCI has several limitations. It has a fixed width of 32 bps and can handle only five devices at a time. A higher bus speed will cause the device to experience problems.

In the 1990s, these devices have become faster and more powerful. The bus graphics evolved from PCI to AGP. The first of this kind were the AGP2X and AGP4X. Today's AGP8X operates at approximately 2 Gbps. However, the demands for AGP bus development are still putting tremendous pressure on the motherboard. The introduction of the PCI Express protocol came as an improvement of the traditional PCI and AGP.

PCI Express operates like a network and not a bus (see text covered by the subtopic below). It makes use of a switch controlling several point-to-point serial connections, leading directly to the devices where the data needs to go. Since each device has its own dedicated connection, there is no longer a need to share bandwidth like the traditional PCI.

PCI Express comes in different standards. These are x, 2x, 4x, 8x, 16x, and 32x. Each of these offers much greater bandwidth than the traditional version.

PCI Express is a serial bus standard. This means transmission of information can be simultaneously done in 2 opposite directions. This feature is enabled because the 1x lane in PCI Express can send data in both directions at the same time.

The table below shows the bandwidths offered, including both single and combined directions:

Common PCI Express buses	Maximum bandwidth	Maximum bandwidth in combined direction
PCI Express 1x	250 Mbps	500 Mbps
PCI Express 2x	500 Mbps	1000 Mbps
PCI Express 4x	1000 Mbps	2000 Mbps
PCI Express 8x	2000 Mbps	4000 Mbps
PCI Express 16x	4000 Mbps	8000 Mbps
PCI Express 32x	8000 Mbps	16000 Mbps

PCI bus

The PCI bus is an Intel-developed local bus standard commonly used for Input/Output (I/O) connections. It connects sound, video, and network cards to the motherboard. Its average speed is about 33 MHz and yields a throughput rate of 133 Mbps.

Advantages of PCI Express

PCI Express allows for much higher speeds than the traditional PCI.
PCI Express allows for less congestion since its bandwidth is not shared in the same way as traditional PCI.
Increased bandwidth means increased system performance. Since data can get into the system much faster and easier, information can also be obtained as quickly as possible.