Computers have often been used as fictional objects in literature, movies and in other forms of media. Fictional computers tend to be considerably more sophisticated than anything yet devised in the real world.
Hactar[?], the computer that designed the cricket-ball-shaped doomsday bomb (that would destroy the universe) for the people of Krikkit[?], also in Douglas Adams's The Hitchhiker's Guide to the Galaxy (please correct this and add more detail - I haven't got the book handy.)