The Accelerated Graphics Port is present only in very few new motherboards; it is being phased out. This was a slot dedicated to enhance the graphics capabilities of the system by allowing a high-speed direct bus to the RAM, unlike PCI, the other prevalent bus. (A bus refers to a channel that is used to transfer data.) It operated at 66 MHz and had a 32-bit width. The AGP specifications have passed through three revisions (AGP 1, 2, and 3). The original AGP specification, now referred to as AGP 1, specified only 1X and 2X speeds. It also mandated an AGP slot that provided 3.3 V. AGP2 extended support to the 4X mode of operation. It also specified an AGP slot that provided 1.5 V, but AGP2 cards could work in the older AGP1 slots. To maintain backward compatibility to AGP1 cards, a Universal AGP Slot allowed cards of both versions to be run in it. AGP3 supported speeds up to 8X and would only work in slots that operated at 1.5 V.
The AGP slots differed in the construction, so that 3.3 V and 1.5 V slots and cards were not compatible: the 3.3 V AGP slot has a par- tition towards the left, while the 1.5 V slot has a partition towards the right. Each of these slots also had a Pro version that extended the slot a bit to the right. The AGP Pro slot was for those cards that needed additional power (which was supplied by the Pro extension). The cards were also similarly-notched. Maximum data transfer speeds offered were: AGP 1X: 266 Megabytes per second; AGP 2X: 533 Megabytes per second; AGP 4X: 1066 Megabytes per second; AGP 8X: 2133 Megabytes/second.