On some machines, certain lights and switches were reserved for use under program control. These were often referred to as sense lights and sense switches. For example, the original Fortran compiler for the IBM 704 contained specific statements for testing and manipulation of the 704's sense lights and switches. These switches were often used by the program to control optional behavior, for example information might be printed only if a particular sense switch was set.
Operating systems made for computers with blinkenlights, for example, RSTS/E and RSX-11, would frequently have an idle task blink the panel lights in some recognizable fashion. System programmers often became very familiar with these light patterns and could tell from them how busy the system was and, sometimes, exactly what it was doing at the moment. The Master Control Program for the Burroughs Corporation B6700 mainframe would display a large block-letter "B" when the system was idle.
Switches and lights required little additional logic circuitry and usually no software support, important when logic hardware components were costly and software often limited.
This baroque style of front panels began to die out in 1964 when Seymour Cray designed his CDC 6600 supercomputer with a very simple and elegant display console containing only 2 CRT displays and a keyboard, replacing all the hundreds of switches, buttons, and blinking lights. The 6600 had support from ten supporting "peripheral processors" whose duties included reading the keyboard and driving the graphics displays.
Early microcomputers such as the 1975 Altair 8800 also relied on front panels, but since the introduction of the Apple II, TRS-80, and Commodore PET during the home computer boom of 1977, the vast majority of microcomputers came with keyboards and connections for TV screens or other monitors.