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Accelerated Graphics Port (AGP)

AGP represents an advancement over previous video interfaces. It allows for more efficient transfer of data between the chipset and the graphics controller. There have been three different connectors used for AGP. These are designed so that only the correct card can be inserted into a given slot. Each connector represents a different standard that includes a different signal voltage and other parameters.

PCI Video Cards

PCI video cards are rarely used for primary video adapters anymore; they are almost always used when built-in video fails or to feed video to second monitors. In the late 1990s, however, there were systems in which the video did come in PCI.

DVI Video

DVI video is becoming more popular, especially as digital flat-panel monitors become more commonplace. DVI video is available mainly in AGP video cards and as built-in video. DVI video can be better and faster than analog video. A computer’s VGA port outputs analog video that the video adapter has converted from digital using a Random Access Memory Digital-to-Analog Converter (RAMDAC) chip. All flat-panel monitors are digital, but those with VGA connectors have to convert the analog signal back to digital. Video that has been converted from digital to analog and back to digital again loses some quality. Therefore, it is best to use a digital flat panel monitor with a DVI output. Early digital flat panel monitors used oddball video connectors: the MDR-20 and the Plug & Display connector. The DVI connectors shown aren’t compatible with these, but a few adapters are available. Search the Internet to find them.

For more information on DVI, or go to matrox.com/mga/ products/tech_info/dvi_backgrounder.cfm.

Older Video Interfaces

The only other interfaces you could run into on PCs built since the mid-1990s are ISA, which fit into ISA slots, and VESA Local (VL) Bus. VL Bus adapters fit only into VL Bus motherboard slots. These rather long slots are found only on PCs from the mid-1990s.

Speed

Video speed comes from the type of AGP port, the chipset, the RAMDAC chip, and the type and amount of video memory. With applications that are used to manipulate images, greater speed and memory amount allows for much faster loading and manipulation of images. Moreover, the faster the RAMDAC chip, the faster the refresh rate. We discuss refresh rates later in this chapter.

podle : Book-PC Repair and Maintenance: A Practical Guide