Chapter 2. System Board Features
AGP Interface
AGP (accelerated graphics port) is a high performance interface directed at 3D graphical display
applications. The AGP signals are similar to PCI bus signals with performance extensions added
specifically for video functions.
AGP basically creates a preferred access port for video devices into system memory. This allows efficient
use of memory resources by mapping system memory as special memory for video use only. One of the
primary applications for this memory mapping is for video texture data storage. Video textures are
basically templates that are stored in memory and then applied to pixel data at the time of rendering.
These textures are typically used in 3D display applications. AGP allows this memory to be mapped from
main memory when needed, thus providing potential for high speed 3D rendering while minimizing system
cost.
The AGP hardware interface is based on the 64-bit PCI definition with the following features added:
Support for deeply pipelined read and writes
Demultiplexed address and data, allowing almost 100% bus efficiency
Timing support for 133 MHz data transfer rates, yielding burst data rates of over 500 MB/sec.
Point-to-point signaling protocol for high speed operation
3.3 V only operation
The AGP connector on the system board is defined as a 124-pin high density custom connector for use by
AGP enabled video devices only. It
does not
support generic PCI devices. For configuration purposes,
an AGP video adapter will appear as a PCI device attached to the corresponding PCI bus.
Chapter 2. System Board Features 9
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