I am no expert but I have been researching these in a bit more detail lately.
To my understanding, they are somewhat custom motherboard setups that are specific to certain models. The software also requires some sort of hardware key to work.
I would certainly be interested in hearing from others who are more knowledgable about the specifics of these machines. I have done my fair share of google search and subsequent reading somewhat prompted by the other member who was considering building one from parts as an alternative to the cost of a complete machine.
My considerations included trying to find emulations for a number of what are no doubt proprietary games.
Anyone else have info to chime in with?