Standard Micro-USB-to-HDMI adapter (five-pin)
The first implementations use the most popular mobile connection (micro USB) and the most popular TV connection (HDMI). Other than the physical connectors, USB and HDMI technology are not being used. It is exclusively MHL signaling through the connectors and over the cable.

Samsung Micro-USB-to-HDMI adapter (eleven-pin)
The Samsung Galaxy S III, and later Galaxy Note II and Galaxy S4, use an adapter and Micro-USB socket with six additional connector pins in order to achieve functional improvements over the 5-pin design:
It supports the use of USB and MHL simultaneously. (Note that the new Samsung 11-pin MHL-HDMI adapter also has a USB On-The-Go port).
Samsung’s Galaxy S III/ Note 2 can power the MHL-HDMI adapter (when used with a non-MHL-compatible-TV). Although this can theoretically also be done with the standard 5-pin micro-USB connector, the Galaxy S III's 11-pin connector is believed to be the first smartphone that supports this functionality.
The socket is incompatible with all current non-Samsung MHL adapters.