Hi. I am a newbie and wondered why the KE-72T had four ports. I thought since the encoder acts as though a real keyboard encoder with the pushbuttons working as keys, all you needed to do was hook the KE-72T up to the PS/2 keyboard port on the computer and everything would work.
That's all you have to do.
Four ports -
PS/2 keyboard port - As you said for hooking the KE-72T to the computer.
PS/2 pass-thru port - For using a PS/2 keyboard on the computer with the KE-72 plugged in.
PS/2 mouse port - For hooking the trackball to the computer.
RS-232 parallel port - Optional interface for programming the unit, but you can also program it through the PS/2 port, AFAIK.
Having said that, while the unit is a solid piece of equipment, it is not designed for arcade controls, and not optimum for MAME.
If you need that many inputs, you could buy an I-PAC/4 an I-PAC/2 and a opti-pac (84 inputs and two trackball interfaces), for about $30 more.
If you can get by with 56 inputs, an I-PAC/4 and an Opti-Pac are slightly LESS expensive than the KE-72T. (And you don't NEED more than 56 inputs, unless you are into 4-player console emulation without using USB gamepads).
If you want to save the most money, the pin-header versions of the KeyWiz Eco, two GP-Wiz Ecos, and one
www.oscarcontrols.com pre-hacked mouse, gives you 96 inputs plus a trackball interface for $82.