CP/M! I still have an 8-inch floppy somewhere in my files for nostalgia's sake from the--what was it? Xerox 820 or something like that? I can't remember whether the files on it are Wordstar or Peachtext. Eventually I switched over to a PC Jr., I think, and meanwhile, I knew a physics professor who used a cutting edge Victor that had double-sided 5.25" floppies and some kind of compression software so that they held more than 640K, if I remember correctly.