The HP 2114 minicomputers had capacitive touch buttons that lit up like elevator call buttons. These were used for loading the boot loader, as well as for a var

The HP 2114 minicomputers had capacitive touch buttons that lit up like elevator call buttons. These were used for loading the boot loader, as well as for a variety of input/output functions. For example, you could insert a "halt" instruction with a code that would get displayed when execution reached that point in your program. You could then increment the program counter register and resume running.