DVI (Digital Visual Interface) was developed by the industry body DDWG (the Data Display Working Group) to send digital information from a computer to a digital display, such as a flat-panel LCD monitor. DVI uses TMDS (Transition Minimized Differential Signaling) to transmit large amounts of digital data from the source to the display, resulting in an extremely high-quality image. In doing so, DVI technology successfully moved from the computer marketplace to the audio/video realm, and is now found on many high-end TVs, DVD players, and HDTV set-top boxes. DVI took a step forward with HDMI, which integrates audio and video into a more compact interface. The DVI interface uses a connector that resembles a DB-style connection. However, instead of round pins, the DVI connector uses flattened pins that appear visually as “twisted” at an angle. This design is referred to as an LFH (low force helix) connector, insuring by way of frictional force of the pins, that a good contact with the mating connector is constant. DVI connectors use thumbscrews for retention and are very reliable. Most DVI connectors have 24 pins and a single larger, offset ground bar. These are called DVI-D interfaces, and carry a digital signal only. Some DVI connectors, called DVI-I, have four extra pins that surround the offset ground bar. A DVI-I interface is designed to carry both digital and analog signals.
DVI-D Dual-link Connector
This connector contains 24 pins, arranged in three horizontal rows of eight pins. To the side of this grouping of 24 pins is a wide, flat pin called a ground bar. A dual-link interface provides two TMDS links, or groups of data “channels” that can carry more than 10 Gbps of digital video information. A dual-link cable is backwards-compatible with single-link applications. The vast majority of DVI applications will use this DVI-D dual-link cable connection.
A single-link DVI connector has 18 pins. The male plug has them arranged in two groups of nine pins, with the flat ground bar off to one side. A single-link interface provides one TMDS link.
This connector appears almost identical to the dual-link DVI-D connector except that it has an additional four pins that surround the flat offset ground bar. This is because the DVI-I interface was originally designed to carry both digital and analog signals, in complete form. However, most DVI displays and video sources are DVI-D, and the female ports do not contain sockets to accept the four extra analog pins. As a result, DVI-I cables are limited to a narrow range of applications such as certain KVM switches. Also note that the offset ground bar on a DVI-I plug is larger than the one on a DVI-D plug. This means that a DVI-I connector cannot fit into a DVI-D socket simply by removing the four analog pins.
This is similar to the dual-link DVI-I, but it carries only a single TMDS link.
DVI-A is not and has never been an “official” standard according to the DDWG. Nevertheless, it is a connector type that allows a VGA device to connect to a DVI-I interface. For instance, the DVI output on a computer’s video card may be DVI-I and thus capable of supporting both digital and analog signals. Many companies have used this deviation in order to connect a VGA monitor. In doing so, a cable or adapter with a DVI-A plug can be used to make the connection. A DVI-A connection has only the pins that carry analog signals loaded into the body of the connector; it is void of all other pins.
HDMI is the acronym for High Definition Multimedia Interface and like DVI-A, is not really a DVI standard but has evolved into an emerging standard of its own. This technology carries the same video information as DVI but adds the capacity for digital audio and control signals as well. The current version of HDMI carries one TMDS link of digital video. It is found on many home-theater/consumer electronics devices, mostly high end but certainly becoming the standard. HDMI, unlike most higher end technology, uses a friction held 19-pin connector; it is fairly easy to disconnect accidently. This connector is formally and technically described as a Type A HDMI connector. The Type B connector is larger (28 pins), but is a prototype and it is not currently used by any devices in the marketplace.