1: Computers still use punched cards.
A collorary to this that no matter how far in the future and how intelligent said computers get, they still seem to whirr and make strange noises. Often they will still have much tape involved. This has its representation in film and TV in an endless number of led’s and dedicated one job only switches.
The ironic thing is that, in said pieces of fiction, the description of the physicality of the computers adds nothing to the plot except a stab at authentic futurism. Computers were fabulously rare after all, the only place the average punter saw one was in a film (cf The Billlion Dollar Brain), so to describe the workings of one genuininely added an air of scientific know-how. This books are still eminently readable, their use of computers after all has nothing to do with how they work, but it adds a strange quaintness when the otherwise alien futurity is bought down to earth with a fifteen cabinet, talk to the card cos the ears aren’t listening bump.
Feel free to list your favourite examples of this in the comments section.