CertiGuide to A+ (A+ 4 Real)  9  Chapter 8: Motherboards

PCI Steering 1 AMR

AGP stands for Accelerated Graphics Port. This is a bus designed to carry specifically video data. Modern video cards plug into an AGP expansion slot on the motherboard. Because video data carries much more information than other types of cards, video cards need their own communication pathway to insure that adequate throughput is provided. Technically speaking, AGP is a port, not an independent bus but AGP does have a dedicated pathway to the CPU. Because video is memory intensive, AGP standards require that the video card contain its own on board RAM. When you hear the terms “video RAM”, “video memory” or “VRAM”, they refer to this type of memory.

Note that in many cases a PCI slot is near the AGP port. The design is such that, if you use the AGP slot, you cannot use the PCI slot next to it, or vice versa.

Modern AGP technology provides a dedicated, high-speed port for the transfer of large amounts of 3D texture data between the graphics controller and the chipset. This prevents data bottlenecks and allows for today’s current graphics intensive applications and games.

While the AGP bus is independent physically from the PCI bus, it is in actuality uses a 66 MHz PCI bus performance extension. The actual AGP slot is similar to a PCI slot but uses a unique connection design that is not compatible with PCI devices. Several AGP specifications have developed over time:

• AGP 1.0 is the original AGP specification.
  
  
• AGP 2.0 was released in 1998 and included modes for 8-byte transfers per two clock cycles, 8-byte transfers per one clock cycle and 16-byte transfers per clock cycle.
  
  
• AGP Pro was designed to deliver additional electrical power to the graphics add-in cards to meet the needs of advanced workstation graphics. AGP Pro slots and circuitry will accommodate AGP 1.0 and 2.0 cards.
  
  
• AGP3.0 offers a significant increase in performance along with feature enhancements to AGP 2.0. This interface represents a further development to existing AGP in order to meet the increasing demands placed on the graphic interfaces within the workstation and desktop.

While AGP 3.0 spec uses existing AGP 2.0 and AGP Pro 1.5v connectors, this does not mean you can use an AGP 3.0 card on an AGP 2.0 motherboard. What this does mean is that some AGP 3.0 motherboards will accept AGP 2.0 and 1.5 depending on the design of the motherboard. Some AGP 3.0 motherboards will support only AGP 3.0 and some will support both AGP 2.0 and AGP 3.0. Failure to pay attention to this fact may result in a dead video card and/or motherboard. Please keep in mind that AGP specification, like the rest of computer technology, are subject to rapid change and this information can be updated at any time. Please review Ian Kayne's Graphic Cards work for more data on APG.

PCI Steering 1 AMR