ESSENTIAL COMMANDS To execute any command on the computer you must type the command and press the return key. The following are commands that interrupt the computer and may be executed at any time: Because they interrupt the computer at unexpected times they should be used with caution. To invoke them you must press both the control key and, at the same time the indicated key. Control/C--This interrupts the operation of a program. Everything that you were doing is lost. Generally a drastic measure taken when all else fails. Control/O--This causes the printout you are receiving to stop being printed although the program continues. Control/S--This causes the printout to stop. Do this if the information is flying by on the screen too fast for you to read it. Control/Q--This reactivates printout. By alternating between Control/S and Control/Q you can control the printout on the screen. Control/Z--This indicates to the computer that it has reached the end of a file. It causes whatever you were doing to stop or abort, but it is much kinder than a Control/C. Control/U--This causes everything you have printed on a line to be deleted. You can then start over. If you have made a mistake in a command that you cannot correct, by pressing Control/U you can start over without having to pass a bad command to the compu- ter. Control/R--Reprints the line you have just typed. Useful when you have made a lot of mistakes and hence deletes and want a clear copy of what you have. Control/T--Gives the run time system characteristics of the program you are running.