Type B HDMI has 29 pins, is about 21mm wide, and has a data clock rate of 330MHz. (It actually uses two 165MHz links, a la the DVI single/dual model.) It's intended for super-high-resolution applications, including theatrical, military and medical imaging applications. Type B HDMI is what you need for compatibility with a dual-link DVI connector—typically for very high-resolution displays.
HDMI, DVI and System Control
HDMI is backward-compatible with DVI; you can readily buy adapters that connect from one to the other. Remember: there's no audio on the DVI side of this connection, so you'll always need to wire sound separately whenever using one of these adapters.
Since HDMI is a pure digital connection, it is only compatible (using an inexpensive adapter cable) with DVI-D or a digital signal running through DVI-I. You cannot adapt an analog signal running through DVI-I.
Unlike DVI, which was more of a computer monitor input format, HDMI is intended as a true home entertainment link, and may also ultimately standardize the proprietary command and control networks that until now were promulgated by many of the major brands (as well as newer "universal" control systems like Mitsubishi's NetCommand). That's right: HDMI can also handle such tasks as automatically turning on the plasma screen and stereo receiver and adjusting each to the appropriate inputs, simply by inserting a DVD into the player. And it can do this regardless of brand.
HDMI was designed to handle cable runs up to 15 meters using standard copper cable. You can add repeaters to achieve longer cable runs, or fiber optic adapters; it's relatively easy and does not affect signal quality.
HDMI is currently on version 1.1. In-Stat/MDR reports some three million TV sets were built with HDMI in 2004, and predicts that by 2006 that total will rise to 20 million, representing 42 percent of the market.