All of these different versions can wreak havoc with custom installations, when seemingly compatible pieces of equipment prove to be incompatible.
Worse, these connectors are moving targets, always susceptible to change, as the case of the broadcast flag demonstrates. If the broadcast flag ultimately does return (by order of a higher court), it presumably will be built into the HDMI interface. Older HDMI connectors may then be rendered obsolete for some purposes. Only time will tell.
Meanwhile, custom installers must deal with today's digital video connections, as well as their legacy predecessors. Here is a guide to at least some of what's out there today.
Digital video interface (DVI)
DVI, the granddaddy of digital video connections, was created by a computer-industry consortium called the Digital Display Working Group. DVI arose after the introduction of LCD monitors as replacements for CRTs. Analog VGA connections—essentially the same as RGB component video connections—made sense for CRTs, but fixed pixel display technologies like LCD operate digitally. It made more sense to feed LCD monitors with a digital signal (rather than converting from digital to analog in the PC and then from analog back to digital in the monitor).
The goal of the computer industry was not just to create a new alternative to the standard 15-pin VGA connector, but to create a true replacement for it, one that could handle both digital and analog video signals. But since that dual-interface capability costs more to build, the spec also provides for a digital-only version that's less expensive.
Thus, the DVI connector has two forms.
DVI-I (DVI-Integrated) is the universal analog and digital connector. The analog connections are arranged in a five-pin cross pattern that's separate from the other 24 pins, and helps visually identify this connector.
DVI-D (DVI-Digital) is the digital-only version. The connector looks almost identical, except the analog pins on the side are missing.