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PCI vs PCIe | difference between PCI and PCIe

This page on PCI vs PCIe mentions basic difference between PCI and PCIe bus interfaces. PCI stands for Peripheral Component Interconnect where as PCIe stands for PCI Express.

PCI Bus

PCI has been part of computer architecture since years. The full form of PCI is Peripheral Component Interconnect.
It has been used to insert various PC cards such as video, sound and network cards to the motherboard. The developments in these cards have become advanced but no development has been made to the PCI bus.

PCI supports bus width of 32 bits and supports 5 devices simultaneously. PCI-X which has been introduced later supports bus width of 64 bits. PCIe as described below has been introduced to overcome the drawbacks of PCI

PCIe Bus

The full form of PCIe is Peripheral Component Interconnect Express. This bus interface supports more BW(Bandwidth) compare to PCI and it supports almost all the existing OSs. PCIe architecture makes computer run faster. It provides superior graphics performance.

PCIe(PCI Express) is basically a serial connection. It operates like network. PCIe will have a switch which controls multiple point to point serial connections. In PCIe architecture, all the devices will have dedicated unique connection so that devices need not have to share BW as they do in a normal bus architecture.

The x1 PCIe connection will have one lane which is composed of 4 wires (2 wires are used in the transmit direction and 2 wires are used in the receive direction). This connection will carry 1 bit/cycle. The other configurations of PCIe are x2, x4, x12, x16 and x32. A x2 PCIe connection will have 8 wires. It transmits 2 bits/cycle.

Difference between PCI and PCIe

Following table mentions comparison between PCI and PCIe interfaces with respect to speed, bus type, topology, number of devices on bus and other parameters.

Specifications PCI PCIe
Bus type Parallel Serial
Data transfer Data can be sent in one direction at a time. Data can be sent in two directions.
Bandwidth It is shared. It is not shared.
Connector size Big Small
Isochronous data transfer Not supported Supported
Scalability Bandwidth can not be scaled. Bandwidth can be scaled.
Advanced power management Not supported Supported
Speed or data transfer rate 133 MB/s to 533 MB/s 250 MB/s to several GB/s per lane, it is different for different specifications
Number of End devices on bus 5 (Maximum) 32 (Maximum)
Topology Shared bus Point to point or shared switch
Hot Plugging Not supported Supported

Also refer advantages and disadvantages of PCI Bus and PCI Express.



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