What is AGP (Accelerated Graphics Port) and how does it work

What is AGP (Accelerated Graphics Port) and how does it work

AGP is the short-term for Accelerated Graphics Port and is concretely a point-to-point bus. The bus, compatible with IBM computers, is hence used as a Local Bus and operates as a Peripheral Component Interface that includes 20 supplementary signals not currently found on a PCI bus.

What is Accelerated Graphics Port (AGP)?

Accelerated Graphics Port (AGP) is a parallel expansion card standard that has been designed to attach a video card to a computer system to assist in the acceleration of 3D computer graphics. Since 2004, AGP inches its way and progressively replace PCI Express (PCIe)

How does it work?

Unlike PCIe technology that has been designed over a shared-memory design, AGP takes advantage of a dedicated memory bus fr graphics hardware.

The AGP bus has a width of 32 bits and works at a full bus speed compared to the normal PCI. AGP specifies mainly for the Protocol, Electrical, and Mechanical parts 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 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 the 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.

What are the 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
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