Cool sidenote: the Dreamcast controllers had two slots. I wonder if they had cool interactions, like the MSX, the SuFami Turbo, and the relatively more modern but more distantly related Metal Gear Solid where Psycho Mantis comments on what other games you've been playing based on the saves on your memory card.

They could probably read the card data (I mean, they would have to in order to load saves off 'em anyway) and do the Psycho Mantis thing. Though I can't recall any of the games I have for it doing it. I do remember one of them being able to determine if the VMU was a full VMU or just a memory card because it wouldn't let you install the little VMU game it had to anything but an actual VMU with a screen. Trying to put it on a 3rd party memory card that didn't have the screen would give an error.