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DVI - Digital Visual Interface

Digital Versus Analog

Digital Visual Interface connections allow users to create a digital-to-digital connection between their display and source. We most commonly see the digital-to-digital connection between flat screen monitors and computers. However, new HDTV set top boxes can be found which offer DVI output.

The signal your television receives with an antenna is analog. Sometimes the picture is fuzzy, sometimes it comes in perfectly clear, and sometimes it fades in and out. With a digital signal, the signal is either on or off, so "fuzziness" is not possible. That is not to say that an analog signal always looks fuzzy. A high quality analog signal also produces beautiful, clear images. The signals are just not quite as consistent as digital..

DVI At-A-Glance:

• DVI is the only current cable that can create a “digital-to-digital” connection.
• Digital signals are comprised of a series of 1's and 0's. By comparison, an analog signal can be partially on or off. For example, an analog signal may measure 0.93 or a 1.09 rather than a 1.
• Some DVI connectors can support both digital and analog signals.

Digital to Analog to Digital -- Computers and Digital Displays

To experience the greatest benefits of using a digital display device, a digital connection is necessary. You may think that when you connect a computer, which is a digital device, to a digital display, you automatically have a digital to digital signal. However, without a digital cable connecting them, it is not the case.

When data from a computer leaves your computer memory, it has to go through what is called a RAMDAC (Random Access Memory Digital to Analog Converter), which converts the signal from digital to analog in order for a VGA or another analog cable to carry the signal to the monitor. Once converted, the VGA cable carries the signal to your monitor. If your monitor is a digital monitor, it has to be converted once more to digital.

Each conversion create small amounts of signal loss which impact the overall quality of the picture. DVI has eliminated the need for these conversions.

DVI to the Rescue

DVI is a relatively new standard, but is quickly being adopted by computer and select television manufacturers. Many expect that DVI will replace VGA as the most common connection for computers to displays.

DVI is capable of processing large amounts of data at high speed, which is one reason for its success. High-bandwidth content like HDTV, and high-resolution display devices are becoming more popular and have outgrown current technology.

DVI Details

One additional benefit of DVI is that it can support both analog and digital connections. DVI-D is a smaller connector, and supports only digital signals. DVI-I is slightly larger and can accommodate both digital and analog signals.

DVI transfers data using what is called the transition minimized differential signaling (TMDS) protocol. The DVI protocol calls for at least one TMDS "link" which has three data channels (RGB) and one clock control channel. In some cases two or "dual" TMDS links may be used to increase the bandwidth of the connection.

DVI Type	Signal Type	Number of Pins
DVI-D	Digital Only - 24 pins (3 rows of 8 pins)	24 pins
DVI-I	Digital and Analog  - 24 pins plus 5 (for analog RGBHV)	24 pins plus 5 for analog (RGBHV)
Dual Link	Dual Link DVI supports 2x165 MHz (2048x1536 at 60 Hz, 1920x1080 at 85 Hz). A dual link implementation utilizes all 24 of the available pins.	24 pins
Single Link	Single Link DVI supports a maximum bandwidth of 165 MHz (1920x1080 at 60 Hz, 1280x1024 at 85Hz). A single link implementation utilizes 12 of the 24 available pins.	24 pins

DVI Type	DVI-D Receptacle	DVI-I Receptacle	DFP Receptacle	VGA Receptacle
DVI-D Plug	Yes	Yes	With Adapter	No
DVI-I Plug	With Adapter	Yes	With Adapter	With Adapter
DFP Plug	With Adapter	With Adapter	Yes	No
VGA Plug	No	With Adapter	No	Yes

Source: http://www.ddwg.org