AGP

Short for Accelerated Graphics Port, an interface specification developed by Intel Corporation. AGP is based on PCI, but is designed especially for the throughput demands of 3-D graphics. Rather than using the PCI bus for graphics data, AGP introduces a dedicated point-to-point channel so that the graphics controller can directly access main memory. The AGP channel is 32 bits wide and runs at 66 MHz. This translates into a total bandwidth of 266 MBps, as opposed to the PCI bandwidth of 133 MBps. AGP also supports two optional faster modes, with throughputs of 533 MBps and 1.07 GBps. In addition, AGP allows 3-D textures to be stored in main memory rather than video memory.

AGP has a couple important system requirements:

  • The chipsetmust support AGP.
  • The motherboardmust be equipped with an AGP bus slot or must have an integrated AGP graphics system.
  • The operating system must be the OSR 2.1 version of Windows 95, Windows 98 or Windows NT 4.0. And currently, many professional Macintoshes support AGP.
  • AGP-enabled computers and graphics acceleratorshit the market in August, 1997. However, there are several different levels of AGP compliance. The following features are considered optional:

  • Texturing: Also called Direct Memory Execute mode, allows texturesto be stored in main memory.
  • Throughput: Various levels of throughput are offered: 1X is 266 MBps, 2X is 533 MBps; and 4X provides 1.07 GBps.
  • Sideband Addressing:Speeds up data transfers by sending command instructions in a separate, parallel channel.
  • Pipelining: Enables the graphics card to send several instructions together instead of sending one at a time.
  • Also see Understanding Video and Graphics Adapters in Webopedia’s “Did You Know…?” section.

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