Difference Between PCI and PCI Express

The Peripheral Component Interconnect or more commonly known as PCI is a standard for connecting a lot of devices inside your computer to extend its capabilities. Devices like sound cards, modems, NIC, TV Tuners, and some video cards have at some point or another have used the PCI port. The latest version of PCI known as PCI express is a much improved version in terms of speed.

PCIe uses a serial interface instead of the old parallel interface used by PCI. It also utilizes individual buses for each of the devices connected to it instead of a shared one like what PCI uses. The difference in speed is quite huge when comparing the standard PCI slot which runs at 133MB/s to a 16 slot PCIe that can send or receive up to 16GB/s.

The most common use for PCIe nowadays is with graphics cards which benefits hugely from the huge bandwidth provided by the interface. PCIe has totally replaced another standard called AGP which was specifically intended for graphics cards.

PCIe wasn’t intended to run at full speed for all devices since most devices don’t really need that much to operate properly. Speeds are categorized by lanes, each with its own transmit and receive lines. Each lane can provide up to a maximum of 1GB/s, thus giving the 16 lane slot the maximum 16GB/s, slower devices are categorized by the number of lanes they use from 1 to 16.

Unlike PCI slots which are the same size for all devices, PCIe slots can differ depending on which form factor it accepts. The longest would be the 16 lane slot and understandably, the shortest is for the x1 devices. Although there are slots that accept multiple form factors but only operate at a lower speed. This is done in order to allow the use of bigger cards in what would otherwise be a smaller slot. Even if the speed doesn’t necessarily match up to what is required, it allows the user a little bit more flexibility in terms of what he can plug into his machine.

Although PCIe is generally superior compared to PCI, there is still a lot of devices that are being made for the PCI slot, due in part to the simplicity of PCI and to the fact that most devices do not really need the significant speed advantage.

Summary:
1. PCIe is much faster compared to PCI.
2. PCIe uses a serial interface while PCI uses a parallel interface.
3. PCIe speed is classified into lanes, each capable of delivering up to 1GB/s data transfer.
4. PCI slots are standardized while PCIe slots vary depending on the number of lanes the slot is intended for.
5. Despite PCIe superiority, most manufacturers still use the PCI standard for their devices.

Further information : http://www.differencebetween.net/technology/difference-between-pci-and-pci-express/