Digital Video Interface (DVI) was a specification developed in 1999 by the Digital Display Working Group (DDWG) in order to standardize digital interfacing. While some DVD players and television sets today may feature DVI connectors in addition to analog Component Video, DVI connectors are mostly found in the computer market as the standard computer interface between LCD monitors and modern video graphics cards. The specification was designed to be flexible and thus included support for both analog and digital interfaces. As a result, there are multiple connector types on the market, and consumers should be aware of the differences and limitations of each.
DVI connectors come in three types: DVI-A (analog), DVI-D (digital) and DVI-I (interlaced; analog and digital). Both DVI-I and DVI-D connectors have two distinct data rates, also known as single-link and dual-link. Each link type has a maximum allowed data rate that ensures data is not corrupted when transferred from the video card to the monitor.
DVI uses Transition Minimized Differential Signaling (TMDS) to transmit data over one twisted wire pair. A single-link DVI connector consists of four TMDS links. Three of the four links correspond to the red, green, and blue RGB video signals, while the fourth is a clock control channel. Single-link connectors operate up to 165MHz and offer 1.65Gbps of bandwidth. They support resolutions up to 1920x1200 at a refresh rate of 60Hz.
Dual-link connections double the number of RGB TMDS pairs – excluding the clock pair – through parallel connections, thus enabling 2Gbps of bandwidth, but with an operation limit of 100MHz. They support higher resolutions up to 2560x1600 at a refresh rate of 60Hz. Dual-link connectors are fully backwards compatible with single-link connections as the specification requires single-link mode operation when display modes use a pixel clock below 165 MHz and have at most 24 bits per pixel. Only if a display mode requires more than 165 MHz pixel clock frequency or 24 bits per pixel will dual-link mode be used. In contrast, a single-link connector cannot support dual-link connections at any time; hence a dual-link connection is preferable in most cases.
DVI connection pins are comprised of the following potential components: parts of an 8x3 rectangle pinout supporting TMDS, DDC, analog vertical sync, power, hot plug detection and ground signals (Pin 1-24); 4 analog pins for RGB and horizontal sync (C1-C4); and a long flat pin for analog ground (C5).
DVI-A connectors have 17 (12+5) pins, do not have a dual-link option, and only carry analog signals. These signals are identical to VGA signals but are presented as an altered configuration. A VGA to DVI adapter is necessary to connect a VGA video card to a DVI-A monitor or a DVI-A video card to a VGA monitor. Due to VGA being the dominant connector for analog monitors and DVI as a standard for digital signals, DVI-A connectors are quite rare; instead, DVI-I (integrated) and DVI-D (digital) connectors are more common. DVI-A cables will work with both DVI-A and DVI-I connectors. Male DVI-D cables may fit in a female DVI-A connector, but will not work as they do not carry any analog signals.
DVI-D connectors can only transfer digital video signals. Single-link DVI-D connectors have 19 pins (18+1) and dual-link DVI-D connectors have 25 pins (24+1). DVI-D cables will work with both DVI-D and DVI-I connectors. HDMI and DisplayPort connectors can support DVI-D video signals through an adapter, but DVI-D cannot support the additional features that HDMI and DisplayPort possess, such as integrated audio and CEC control. Most digital monitors have a DVI-D connector, while monitors which support both digital and analog signals usually have a DVI-D and VGA connector. Note that female DVI-D connectors will not accept male DVI-A or DVI-I cables as those connectors have the additional 4 analog pins that DVI-D lacks.
DVI-I single-link connectors have 23 pins (18+5) and dual-link connectors have 29 pins (24+5). DVI-I connectors do not convert analog and digital signals but can accept digital or analog signals – just not both at the same time. If a video card, monitor and cable all have DVI-I connections with the ability to support both analog and digital signals, one mode of operation has to be chosen. True to their purpose, DVI-I connectors will work with all three DVI cable types. However, a male DVI-I cable will not fit in a female DVI-D connector due to its additional analog pins. Hence, when considering the rarity of a DVI-A connector, a DVI-D cable is the most commonly applicable out of the three cable types.
In addition to the standard DVI connectors, Apple developed a Mini-DVI connector for some of its computers as a compact digital alternative to the Mini-VGA connector. The connector can be found on Apple's 12-inch PowerBook G4, Intel-based iMac, Intel-based MacBook laptop, Intel-based server, and the 2009 Mac mini. The Mini-DVI connector features a significantly distinct pinout from standard DVI connectors, with 32 pins spanning an 8x4 rectangle. The connector is able to transfer DVI, VGA and TV signals via adapters. Its inability to support dual-link connections limits its maximum resolution to 1920x1200 at 60Hz. In October 2008, Apple announced its plans to phase out the Mini-DVI and replace it with the Mini DisplayPort, which supports higher resolutions up to 2560x1600 (WQXGA) and can be found on all new Macintosh computers.
While Mini-DVI connectors are no longer being implemented, standard DVI connectors, particularly DVI-I and DVI-D ones, are still widely used in the computer market for video graphics cards and LCD monitors. Discerning consumers should be able to distinguish between the different types of connectors and cables they have and understand the limitations of each in order to determine and implement the system configuration they desire.
About Video Products Inc
Video Products Inc (VPI), based in Aurora, OH (USA), is dedicated to supplying the highest quality connectivity products to integrators, distributors, IT professionals, and tech-savvy home-users. VPIs product line includes a wide variety of cables, adapters, hubs, switches and splitters. All products are rigorously tested and are backed with a one-year warranty on all parts and labor, and a 30-day satisfaction guarantee. For more information, visit www.vpi.us