The 512 being the Fat Mac. "Fat," because 512 is so much more than 128.
That was my second computer, purchased only a couple of years after my Osborne. Things were changing really fast just then and the Mac was a huge leap in usefulness. Don't have that one anymore, though. It went into a dumpster in 1992 after it stopped working. Wasn't worth trying to fix by then, of course.