Peripheral Component Interconnect (PCI) is a 32-bit parallel bus that normally runs at a maximum of 33 MHz. While it has provided a stable and flexible platform for hardware and software developers to build on for almost a decade we are starting to reach the limits of this parallel bus with the new modern computers.

PCI-Express is intended to be an evolutionary upgrade to the existing PCI bus. It will maintain complete hardware and software compatibility with all recent PCI devices. In terms of form though, it is something completely new and was approved as a standard in April of 2002.


The PCI-Express is not a single parallel data bus through which all data is routed at a set rate. PCI-Express is an assembly of serial, point-to-point wired, individually clocked ‘lanes’ each consisting of two pairs of data lines that carry data upstream and downstream.

PCI-Express is a 2-way, 2-bit wide serial connection that carries data in packets, similar to the way it is transferred over Ethernet connections.

The real performance benefit comes in when more than one lane is added to a given point-to-point route. Lanes can be stacked together to increase the amount of bandwidth available to specific areas of the I/O system, such as the video card slot


PCI Express X1
Eventual PCI card replacement
Typical x1 devices will be network and modem cards, etc.
x1 bandwidth is 500MB/s bidirectional vs. 133MB/s for 32-bit / 33MHz PCI.

PCI Express X16
AGP replacement
The AGP bus tops out at 2 GB/sec. bandwidth (AGP 8x) while PCI-E x16 is designed to provide 8GB/sec. bidirectional of bandwidth

Peripheral Component Interconnect (PCI) slots are such an integral part of a computer's architecture that most people take them for granted. For years, PCI has been a versatile, functional way to connect sound, video and network cards to a motherboard.



But PCI has some shortcomings. As processors, video cards, sound cards and networks have gotten faster and more powerful, PCI has stayed the same. It has a fixed width of 32 bits and can handle only 5 devices at a time. The newer, 64-bit PCI-X bus provides more bandwidth, but its greater width compounds some of PCI's other issues



A new protocol called PCI Express (PCIe) eliminates a lot of these shortcomings, provides more bandwidth and is compatible with existing operating systems. In this article, we'll examine what makes PCIe different from PCI. We'll also look at how PCI Express makes a computer faster, can potentially add graphics performance, and can replace the AGP slot.