Ati x cards are pci express as i have one, the main difference in the pcie, pcix, and pci express are in the bandwidth to the motherboard from the card.
From what i have read mind you this might not be correct info because i did read it online. All the cards can support different bandwiths ranging from 4x, 6x, 8x, 10x, 12x, and 16x. The pcie and pcix usually support the lower bandwidths between 4x and 8x, and pci express supports the higher ones 10x to 16x. Again though this is just something i read online and it was awhile back before i decided to buy my new comp also at the time nvidia didn't have a pcix or express on the market, so the cards may have changed by now.
But i do know that the ati x600 xt 128 is 16x as im using one currently.
While i couldnt find the article that i read before i did find this.
Introduction
The venerable PCI Bus has been one of the bastions in PC connectivity for roughly a decade now. The limitations of the PCI bus was first highlighted with the introduction of the ubiquitous AGP port back in the summer of 1997.
The main advantages of AGP are its increased bus speed / bandwidth as well as its point to point architecture. A point to point protocol means that AGP has its own path way to communicate with the processor as well as one to the memory whereas every device on the PCI bus had to share the 133 MB/s worth of bandwidth allocated to it. Both the AGP and PCI Bus are based on a 32 bit bus. AGP being clocked at 66 Mhz versus 33 for PCI had double the bandwidth (266 MB/s) in its first iteration. With the ability to transfer data multiple times per clock cycle, AGP in recent times (currently at a maximum of 8x, has ~2100MB/s of bandwith).
With a bevy of high speed I/O devices today outside of the graphics card including SATA / ATA150 (150 MB/s), Gigabyte Ethernet (125 MB/s), 1394B (100 MB/s) it is easy to see that any one of these devices alone can completely saturate the PCI bus completely. Nearly everything else in the PC has scaled in one way or another in the past decade except for the PCI bus. With the exception of PCI-X (a 64 bit, 66 Mhz, server solution), the PCI bus has stayed relatively stagnant while many of the subsystems have been scaling up (frontside bus speed, memory, AGP). Fortunately, this is about to change with the advent of PCI Express.
PCI Express
PCI Express (not to be confused with PCI-X) is the upcoming replacement for both PCI and AGP. A couple of main points about PCI Express
While the classic PCI Bus is based upon a parallel architecture, PCI Express is serial based, drastically reducing pin count.
It is a point to point protocol much like AGP. Devices do not share bandwidth
