The CEPS (Color Electronic Prepress Systems) like Scitex and Crossfield generally output 4-color separation negatives (CMYK). A lot of art was involved in the creating K separation; things like GCR (gray component replacement) and undercolor removal. In addition, there were a lot of fancy algorithms involved in creating the size and shape of the half-tone dots.
Originally Posted by AgX
Scitex started computerizing things very early in the '80s.