In 1982 a CRAY mainframe computer had 8MB of memory at a cost of
$7,000,000. For TRON, each rendering required 18MB of memory, so even on
a CRAY the animators could not have viewed a single frame. For
whatever computer they used, they had to render one scan line at a time and could not see the results of their efforts until the scan lines
were combined on to film.