Word processors never display a cursor.
You never have to use the space-bar when typing long sentences.
All monitors display inch-high letters.
High-tech computers, such as those used by NASA, the CIA, or some such governmental institution, will have easy to understand graphical interfaces. Those that don't, have incredibly powerful text-based command shells that can correctly understand and execute commands typed in plain English.
Corollary: you can gain access to any information you want by simply typing ACCESS ALL OF THE SECRET FILES on any keyboard.
Likewise, you can infect a computer with a destructive virus by simply typing UPLOAD VIRUS (see Fortress).
All computers are connected. You can access the information on the villain's desktop computer, even if it's turned off.
Powerful computers beep whenever you press a key or whenever the screen changes. Some computers also slow down the output on the screen so that it doesn't go faster than you can read. The really advanced ones also emulate the sound of a dot-matrix printer. (see The Hunt For Red October or Alien)
All computer panels have thousands of volts and flash pots just underneath the surface. Malfunctions are indicated by a bright flash, a puff of smoke, a shower of sparks, and an explosion that forces you backwards.
Corollary: sending data to a modem/tape drive/printer faster than expected causes it to explode.
People typing away on a computer will turn it off without saving the data. (see the opening credits for The Hunt For Red October)
A hacker can get into the most sensitive computer in the world before intermission and guess the secret password in two tries.
Any PERMISSION DENIED has an OVERRIDE function (see Demolition Man and countless others).
Complex calculations and loading of huge amounts of data will be accomplished in under three seconds. Movie modems usually appear to transmit data at the speed of two gigabytes per second.
When the power plant/missile site/whatever overheats, all the control panels will explode, as will the entire building.
If a disk has got encrypted files, you are automatically asked for a password when you try to access it.
No matter what kind of computer disk it is, it'll be readable by any system you put it into. All application software is usable by all computer platforms.
The more high-tech the equipment, the more buttons it has (Aliens). However, everyone must have been highly trained, because the buttons aren't labelled.
Most computers, no matter how small, have reality-defying three-dimensional, active animation, photo-realistic graphics capability.
Laptops, for some strange reason, always seem to have amazing real-time video phone capabilities and the performance of a CRAY Supercomputer.
Whenever a character looks at a VDU, the image is so bright that it projects itself onto his/her face (see Alien, 2001, Jurassic Park).
If you display a file on the screen and someone deletes the file, it also disappears from the screen. There are no ways to copy a backup file - and there are no undelete utilities.
Computers never crash during key, high-intensity activities. Humans operating computers never make mistakes under stress.
No matter what kind of virus it is, any computer can be infected with it - even an alien spaceship's computer - simply by running a virus upload program on a laptop (see Independence Day).
You cannot stop a destructive program or virus by unplugging the computer. Presumably the virus has it's own built-in power supply.
You cannot stop a destructive program downloading onto your system by unplugging the phone line. You must figure out the mandatory "back door" all evil virus programmers put in.
Computers only crash if a virus or a hacker is involved.
All text must be at least 72 point.
Word processors do not have an insert point.
The only way to reboot is to shut off the main power to the building.
Passwords can be guessed in three and exactly three tries. If you cannot guess the password in three tries, you must give up immediately.
Any task or program can be executed by simply pressing Enter, no matter which program or window is in the foreground.
All scanners, video cameras and digital cameras have a resolution of approximately 500 megapixels. Any image can be infinitely magnified with no pixelization.
Security will not improve over time. Nonaffialiated personnel can take over a space ship without needing an account or access control. Corollary: Anyone can override access control lists in the future.
All hackers wear black T-shirts or Hawaiian shirts.
Incoming messages are displayed letter by letter. Email over the Internet works like telegraphs.
Microsoft Windows doesn't exist. Macintosh has at least 75% market share.
GUI operations, such as image selection and manipulation, can be handled easily and quickly via the keyboard.