Sense switch

A sense switch or program switch, is a switch on the console of a computer whose state can be tested by conditional branch instructions in software. Most early computers had several sense switches. They were typically used by the operator to set program options.

These bit-switches were more normally used with the computer stopped to specify some memory address to be viewedvia the indicator lights on the console or to be loaded with some value via a second setting of the bit switches and much manipulation of the console. 

Nevertheless their state could be determined by a suitable machine code routine arranged so as to be callable from a compiler language such as fortran, and so a running programme might modify its behavior amount of progress information printed, the tactics of a multi-variable optimization attempt, and so on.

With the introduction of personal computers where the user is once again in attendance of the computer instead of being walled off by a batch-job arrangement, the user would once again be able to adjust switches but alas there are no longer sense switches attached to the computer to adjust.