Systems supported:
- 400 series with ASCII keyboard, 32x32 Model 440 video, 5.25" or 8"
  floppy.
- 500 series with polled keyboard, 64x32 Model 540 video, 5.25" or 8"
  floppy, optional 540B color mode screen driver.
- 600 series with inverse polled keyboard, 64x16 video, 5.25" or 8"
  floppy.
- 500 series based serial based systems with 8" floppy drives, loadable
  VT100 screen driver.