Take a glance at the back of your computer: It may look like a children's toy. Here are a series of funny-shaped holes, and it's up to you to plug a few pegs in. Only with a computer, the pegs are expensive -- things like HD monitors, which connect to your computer using a digital video interface, or DVI port. The DVI port is necessary for digital output to a digital screen.
Most video signals in the United States are digital. You may remember a bit of fuss about digital video in 2009, when television broadcasters switched from the old analog video standard to full digital broadcasts, prompting anyone without a digital receiver to purchase one to watch cable. Computers have always produced digital video, but computer monitors weren't always ready to receive it, so video cards within computers converted digital picture information into analog pulses to display on computer monitors. When digital monitors became widely available, however, computers could output digital video and do so through DVI ports.
Types of DVI
DVI comes in three different formats: DVI-Digital (or D), DVI-Analog (A) or DVI-Integrated (I). Analog DVI ports are pretty common in older computers that connected to cathode-ray tube (CRT) monitors. These ports are trapezoidal and have 15 pins -- a standard monitor connector. DVI-D, by contrast, has differently shaped pins arranged in three even rows with a larger, flat pin beside them. DVD-I combines both port types and outputs both kinds of signals, for greater compatibility.
You'll find DVI-D ports in computers with HD graphics cards. These cards output digital video signals at high resolutions to digital monitors. Not all DVI-D connections send HD signals, but the major distinction between analog and digital video is the higher resolution output of digital signals. A standard video card doesn't offer the same kind of output; likewise, you can't connect an analog monitor to a DVI-D port without using a converter.
For a complete digital video setup you need a computer with a DVI-D port, a digital monitor (any LCD or LED monitor) and a cable to connect the two devices. DVI-D cables come in a few different lengths, and as with any video device the length of the cable matters. The official DVI specifications indicate that signal strength (and, therefore, picture quality) deteriorates after 16 feet, which should only be an issue when using an HDTV in a separate room from your computer as a display.