A colleague of mine - knowing about my interest for ancient computers - recently asked me whether I knew which system they were using in the 1968 movie "Hot Millions" with Peter Ustinov. I remember having seen this picture once, and I also remember they had a mainframe in the scenery. But the only image I could look up in internet is this one with Ustinov sitting in front of a terminal. I guess I will have to watch "Hot Millions" again in order to find out.
Anyway, this question caught my attention, so I did some more research and discovered that the first appearance of a computer in a cinema movie was probably a mockup named "EMERAC" (reminiscenting about ENIAC or UNIVAC?) in "Desk Set" with Katherine Hepburn from 1957. It even consisted of real computer parts, namely IBM 704 magnetic tapes and some panels from the famous SAGE military computer (based on vacuum tubes and ferrite core memory).
No list of computers in old movies would not be complete without HAL9000 from "A Space Odyssey". Timeless.