Accelerated Graphics Port
The Accelerated Graphics Port (AGP, also often called Advanced Graphics Port) is a high-speed computer bus standard for attaching peripheral devices to a computer motherboard, dedicated primarily to assist graphics cards in the acceleration of 3D computer graphics.AGP dynamically allocates the PC's normal RAM to store the screen image and to support texture mapping, z-buffering and alpha blending.
AGP originated from Intel, and that company originally built AGP into a chipset for its Pentium II microprocessor in 1997. AGP cards generally slightly exceed PCI cards in length. AGP became common in mainstream systems in 1998.
The first version of AGP, now called AGP 1x, uses a 32-bit bus operating at 66 MHz. This results in a maximum data rate for an AGP 1x slot of 266 megabytes per second. In comparison, a standard 32-bit 33 MHz PCI bus (which can be composed of one or more slots) maxes out at 133 MB/s.
As of 2003, newer versions of AGP increase the transfer rate dramatically from two to eight times. Available versions include AGP 2x, AGP 4x, and AGP 8x. In addition, AGP Pro cards of various types exist. They usually require higher voltages and some take up the space of two cards in a standard computer (though they only connect to one AGP slot).
AGP allows for efficient use of frame buffer memory, thereby helping 2D graphics performance as well. In fact, many RAID systems for "headless" (that is, lacking an attached display) servers plug into the empty AGP slot to take advantage of its increased throughput as opposed to PCI.
AGP provides a coherent memory management design which allows reading scattered data from system memory in rapid bursts. AGP allegedly reduces the overall cost of creating high-end graphics subsystems by using existing system memory. However, general system memory, although cheap, performs much slower than dedicated on-card graphics RAM, and both mid-range and high-end graphics cards rely on their own high-speed RAM for performance. Cheap low-end graphics cards with little on-board RAM benefited from AGP early in the life-cycle of the technology, but the lowered cost of memory since about 2000 has led to even low-end cards having 64MB or 128MB of dedicated RAM, and thusly graphics now rarely utilise system RAM.
AGP usage should phase out by around 2005, since Intel have indicated that their future chipsets (scheduled for introduction in mid-2004) will replace AGP support with PCI-Express. Nvidia's upcoming NV40 will be their last graphics processing unit to support AGP, and similarly ATI's upcoming R420 GPU will be their last natively AGP chip. Both companies have stated that no further AGP chipsets will be made by them.
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This article was originally based on material from the Free On-line Dictionary of Computing and is used with permission under the GFDL.