Expansion Cards Part 2: AGP
Expansion Cards Part 2: AGP
Expansion Cards Part 2: AGP
The first in this series of Tech Tips on expansion cards took a look at the PCI slot, and the variety of devices that may find their home in one. Graphics cards are one of the many items that may be used in a PCI slot, but the demands of fast-paced video games require more speed and greater bandwidth than the PCI Bus can provide. Thus, the AGP slot was born, providing a dedicated interface to transfer graphics data only.
The letters ‘AGP’ stand for Accelerated Graphics Port, and it is the term used to describe a dedicated, point-to-point interface that connects a video card directly to the system’s memory and processor.
AGP was first introduced by Intel in 1996, and is based off of their previous work in developing the PCI bus. Despite being based on PCI technology, the AGP and PCI slots on a motherboard are not interchangeable, so an AGP card can not be installed into a PCI slot, and vice versa.
The initial release of AGP saw a sizeable performance boost over PCI, and the few revisions to the standard helped increase this even more as years went by. Other than having a dedicated path to the system’s memory and processor, several other design features help AGP outperform PCI when it comes to graphics performance. Three of the other advancements: pipelining, side band addressing and graphics address remapping table are described below.
Data transfer is improved through ‘pipelining’, a term used to describe Шторы the ability of an AGP graphics card to receive, and act upon, multiple instructions simultaneously. PCI data transfers require each piece of necessary information to be received separately before acting on any of it.
Something called ‘side band addressing’ also provides AGP with a performance boost. Basically, additional lines of data are included with each packet to instruct the system as to where this data is to be used. PCI data transfers do not have this addressing information, and the system must look at the data itself in order to determine its destination. This is an obvious time saver, as well as a resource saver since the processor doesn’t have to analyze all data just to determine the address.
AGP allows the operating system to store texture maps
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