What is Accelerated Graphics Port (AGP)?

Accelerated Graphics Port Definition and Details on AGP vs PCIe & PCI

Photo of an EVGA GeForce 6200 AGP 8X Graphics Card
EVGA GeForce 6200 AGP 8X Graphics Card. © EVGA

Accelerated Graphics Port, often abbreviated as AGP, is a standard type of connection for internal video cards.

Generally, Accelerated Graphics Port refers to the actual expansion slot on the motherboard that accepts AGP video cards as well as to the types of video cards themselves.

Accelerated Graphics Port Versions

There are three common AGP interfaces:

  • AGP 1.0 - 66 MHz, 3.3 V, 1X and 2X, 266 MB/s and 533 MB/s
  • AGP 2.0 - 66 MHz, 1.5 V, 4X, 1,066 MB/s
  • AGP 3.0 - 66 MHz, 0.8 V, 8X, 2,133 MB/s

The first number above is the clock speed of that interface, followed by the voltage requirement, speed, and transfer rate (basically, the bandwidth).

Note: The 1X, 2X, 4X, and 8X numbers indicate the bandwidth speed in relation to the speed of AGP 1.0 (266 MB/s). For example, AGP 3.0 runs at eight times the speed of AGP 1.0, so its maximum bandwidth is eight times (8X) that of AGP 1.0.

Microsoft has named AGP 3.5 Universal Accelerated Graphics Port (UAGP).

What is AGP Pro?

AGP Pro is an expansion slot that's longer than that of AGP and has more pins, providing more power to the AGP video card.

AGP Pro may be useful for power-intensive tasks, like very advanced graphics programs. You can read more about AGP Pro in the AGP Pro Specification [PDF].

Differences Between AGP and PCI

AGP was introduced by Intel in 1996 as a replacement of the slower Peripheral Component Interconnect (PCI) interfaces.

AGP provides a directly line of communication to the CPU and RAM, which in turns allows for quicker rendering of graphics.

One major improvement that AGP has over PCI interfaces is how it works with RAM. Called AGP memory, or non-local memory, AGP is able to access the system memory directly instead of relying solely on the memory of the video card.

AGP memory allows AGP cards to avoid having to store texture maps (which may use lots of memory) on the card itself because it stores them in system memory instead. This means not only that the overall speed of AGP is improved versus PCI, but also that the size limit of texture units is no longer determined by the amount of memory in the graphics card.

A PCI graphics card receives information in "groups" before it can use it, instead of all at once. For example, while a PCI graphics card will gather the height, length, and width of an image at three different times, and then combine them together to form an image, AGP can get all of that information simultaneously. This makes for quicker and smoother graphics than what you'd see with a PCI card.

A PCI bus normally runs at a speed of 33 MHz , allowing it to transfer data at 132 MB/s. Using the list from above, you can see that AGP 3.0 is able to run at twice that speed and transfer data much quicker.

Note: While AGP replaced PCI for graphics, PCIe (PCI Express) has been replacing AGP as the standard video card interface, having nearly completely replaced it by 2010.

AGP Compatibility

Motherboards that support AGP will either have a slot available for an AGP video card or will have on-board AGP.

AGP 3.0 video cards can be used on a motherboard that supports AGP 2.0 only, but it will be limited to what the motherboard supports, not what the graphics card supports. Some motherboards that use only AGP 3.0 may not support the older AGP 2.0 cards.

Universal AGP slots are available that support both 1.5 V and 3.3 V cards, as well as universal cards.

Some operating systems, like Windows 95, don't support AGP due to a lack of driver support. Other operating systems, like Windows 98 through Windows XP, require a chipset driver download for AGP 8X support.

Installing an AGP Card

Installing a graphics card into an expansion slot should be a pretty simple process.

You can see how this is done by following along with the steps and pictures in this Installing an AGP Graphics Card tutorial.

If you're having problems with a video card that has already been installed, consider reseating the card. This goes for AGP, PCI, or PCI Express.

Important: Check your motherboard or computer manual before you purchase and install a new AGP card. Installing an AGP video card that is not supported by your motherboard will not work and may damage your PC.