There are three HDMI connector types with Type A and Type B defined since the HDMI 1.0 specification and Type C defined since the HDMI 1.3 specification.
The Type A connector has 19 pins with bandwidth to support all SDTV, EDTV, and HDTV modes. The plug's outside dimensions are 13.9 mm wide by 4.45 mm high. Type A is electrically compatible with single link DVI-D.
The Type B connector has 29 pins (21.2 mm by 4.45 mm) and can carry double the video bandwidth of Type A for use with very high-resolution future displays such as WQUXGA (3840x2400). Type B is electrically compatible with dual link DVI-D but has not yet been used in any products.
The Type C mini-connector is intended for portable devices. It is smaller than the Type A connector (10.42 mm by 2.42 mm) but has the same 19 pin configuration. (The number of pins are the same but the signal assignment is different because of the different shielding requirements due to the signals being in a single row. The differences are:
All positive signals of the differential pairs are swapped with their corresponding shield,
DDC/CEC Ground is assigned to pin 13 instead of 17,
CEC is assigned to pin 14 instead of 13,
The reserved pin is assigned to pin 17 instead of 14.)
It can be connected to a Type A connector using a Type A-to-Type C connector cable.
Picture source http://electronics.howstuffworks.com/hdmi.htm/printable