Sense switch

[2] IBM's Fortran language, first released for the 704, included statements to test the switches and set or reset the lights.

These bit-switches are more normally used with the computer stopped to specify some memory address to be viewed (via the indicator lights on the front panel), or set.

The state of these switches can be determined by a program, and so a running program might modify its behavior depending on the switches, such as change the amount of progress information printed, alter the tactics of a multi-variable optimization attempt, and so on.

In the more usual batch job environment, it was pressed by the computer operator to signal the operating system to terminate a running program that had perhaps overrun its allowed time, or commenced misbehavior such as repeatedly printing blank lines.

Personal computers replace the function of fixed sense switches with the keyboard and screen user interface.