The Accelerated Graphics Port
Before we had PCI Express, we had the Accelerated Graphics Port (AGP), which represented a step up from the bottlenecked PCI bus. The conception of this port was due to the limitations of PCI and the ever-increasing burdens of heavy graphics processing.
The advantage over the older technology was that AGP cards had direct access to the processor, rather than sharing resources with an entire PCI bus. AGP cards could also read textures loaded in the system RAM directly. PCI cards copied the textures from the RAM and placed them into their local framebuffers first, slowing down the rendering process.
AGP's reign didn't last long. PCI Express finally came along in 2004. Until then, the AGP slot offered a rate of 266 MB/s when it was first introduced. Some of the early graphics processors that supported AGP included the 3dfx Voodoo Banshee (even though it ran in PCI mode), Nvidia's RIVA 128, Rendition's Vérité V2200, and the ATI Rage-series.