Displays had fewer pixels in that era. Files were much smaller (the video and mp3 files we have now would have been considered insanely large back then).
To illustrate: a 3.5" high-density floppy disk holds 1 second of DVD-quality video.
(yes, I know, it depends on the rate of change in the image since modern video codecs are incremental -- I'm going by data rate rather than effective compression ratio)
