Wednesday, January 03, 2007

DVI Video Standard

Digital Video Interface (DVI) - What is it?


DVI is one of the video standards for the emerging field of digital video. As you get newer televisions, HDTV boxes, video cards for PCs, and other video equipment, you may see this type of connector more and more.

The connector is shaped vaguely like a D-Sub connector, with screws on either side to hold it mounted. It has up to 24 pins in the middle, plus four pins possibly around a bar to one side. I say "up to 24 pins" and "possibly around a bar" because there are actually several types of DVI connectors possible.

Three DVI signal types

In instruction booklets that reference the DVI cables you need, you may see a letter after DVI, like this: "DVI-D". There are actually three different types of DVI: DVI-A, DVI-I, and DVI-D. The -A is for analog only, the -D is for digital only, and the -I has both analog and digital pins. How can you tell the difference? The easiest way is to look at the bar at one side of the connector. The four pins around it are for analog signals, so if you do not have those pins, the connector is a DVI-D: it only includes digital lines. If you do have pins around the bar, and most of the pins in the center (there may be a strip of pins missing in the middle. More on this in a second), you probably have a DVI-I connector. If you only have 12 of the middle pins, you probably have a DVI-A connector.

On a male connector, usually on a DVI cable, it is important to know which type it is because if you try to plug a connector into a female port that doesn't have enough holes for the pins, then some of the pins may bend, destroying the cable. On the other hand, female DVI-I connectors can accommodate both DVI-D and DVI-A connectors because they have holes for all of the pins. Most newer DVI equipment is coming with DVI-I connectors standard for that reason.

Single Link and Dual Link DVI

Single Link and Dual Link has to do with how many channels of transmission are available in a cable assembly. You can visually tell a single link male connector from a dual link by the centermost vertical strip of pins. If they are missing, then the cable is single link only. If they are there (meaning all 24 pins are present), then the cable is dual link.

Contrary to many beliefs, dual link isn't really "better", in that the picture quality is the same. Dual link is primarily for getting up to very high resolutions, usually too high for most TVs to get to. Dual link DVI can reach a resolution of 2048 x 1536 at 60 Hz Refresh Rate, sometimes called QXGA or Quad Extended Graphics Array. In most commercial cases, this isn't necessary.

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