What Is Accelerated Graphics Port?


What Does Accelerated Graphics Port (AGP) Mean?

An accelerated graphics port (AGP) is a point to point channel that is used for high speed video output. This port is used to connect graphic cards to a computer’s motherboard. The primary purpose of an AGP is to accelerate 3D graphics output for high definition video. AGP provides much faster connectivity and throughput compared to PCI. An AGP is primarily designed to be used for 3D graphics, high definition games and engineering/architecture graphics.

Accelerated Graphics Port is a parallel expansion card standard, designed for attaching a video card to a computer system to assist in the acceleration of 3D computer graphics. It was originally designed as a successor to PCI-type connections for video cards.

Characteristics of Accelerated graphics port

  • It has high quality and very fast performance.
  • It has a direct path to the PC’s main memory.
  • It connects to the CPU and operates at the speed of the processor bus.
  • It sends video information more quickly to the card for processing.
  • It uses the main memory to hold 3D images.

How does it work?

The AGP bus has a width of 32 bits and functions at a full bus speed compared to the normal PCI. AGP specifies mainly for the Protocol, Electrical and Mechanical part of the bus and uses 1.5 or 3.3 Volt signals. If installed on a Pentium II motherboard, the AGP can run up to 66 MHz with a minimum bandwidth of 254.3 MB/s.

AGP makes use of a particular signaling that allows the user to send a double amount of data over the port at an equal clock speed. The bus hence sends the information on the rising edge, defined as the “0” to “1” transition signal and falling edge of the clock, defined as the “0” transition signal. It consequently makes transitions by using both signals compared to the normal PCI that transfers data on individual transitions at each cycle.

Different AGP buses

  • AGP 1x uses a 3.3/1.5 V signal swing over a bandwidth of 266MB/s
  • AGP 2x uses a 3.3/1.5 V signal swing over a bandwidth of 533MB/s
  • AGP 4x uses a 1.5 V signal swing over a bandwidth of 1066 MB/s
  • APG 8x uses a 0.8 V signal swing over a bandwidth of 2.1 GB/s

Accelerated Graphics Port Versions

There are three common AGP interfaces:

AGP Version Comparison Table
InterfaceClock SpeedVoltageSpeedTransfer Rate
AGP 1.066 MHz3.3 V1X and 2X266 MB/s and 533 MB/s
AGP 2.066 MHz1.5 V4X1,066 MB/s
AGP 3.066 MHz0.8 V8X2,133 MB/s

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), but its transfer rate, voltage requirement, and other details are identical to AGP 3.0.

Differences Between AGP and PCI

AGP was introduced by Intel in 1997 as a replacement of the slower Peripheral Component Interconnect (PCI) interfaces. AGP provides a direct line of communication to the CPU and RAM which in turns allows for quicker rendering of graphics.https://2f452b8038d41f53cc281b6bc51c2813.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

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 table from above, you can see that AGP 3.0 is able to run at over 16 times that speed to transfer data much quicker, and even AGP 1.0 exceeds the speed of PCI by a factor of two.

While AGP replaced PCI for graphics, has been replacing AGP as the standard video card interface, having nearly completely replaced it by 2010.


The primary advantage of AGP over PCI is that it provides a dedicated pathway between the slot(s) and the processor rather than sharing the PCI bus. In addition to a lack of contention for the bus, the direct connection allows for higher clock speeds.

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