For the last ten years the PCI Bus has been the PC connectivity stalwart, but in 1997 the AGP port brought into view its many limitations.
The AGP port brought with it increased bus speed / bandwidth and its point to point protocol meant AGP used its own pathway to communicate with the central processing unit of your PC and your computer’s memory. This was in contrast to the PCI bus where all the devices connected to your computer share the 133 MBs of bandwidth available to it. AGP and PCI Bus are based on 32 bit bus but AGP at 66 Mhz had double the bandwidth of PCI at 33Mhz. AGP presently has the ability to transfer data at a maximum of 8x, has ~2100MB/s of bandwidth). There are several high speed I/O devices available today like SATA / ATA150 (150 MB/s), Gigabyte Ethernet (125 MB/s), 1394B (100 MB/s) and any one of them can easily outdo the PCI Bus. However, with the introduction of PCI Express this is about to change.
So what is PCI Express?
PCI Express is the replacement for both the current version of PCI and the AGP system, but how is PCI Express different from what has gone before and why is it superior?
* Classic PCI Bus technology was based upon a parallel architecture while the new PCI Express is serial based. This feature drastically reduces pin count.
* PCI Express is a point to point protocol much like AGP, so the devices on your PC do not have to share bandwidth
