Front Panel

A front panel was used on early electronic computers to display and allow the alteration of the state of the machine's internal registers and memory. The front panel usually consisted of arrays of indicator lamps, toggle switches, and push buttons mounted on a sheet metal face plate. In early machines, CRTs might also be present (as an oscilloscope, or, for example, to mirror the contents of Williams-Kilburn tube memory).

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.

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.

This baroque style of front panels began to die out in 1964 when Seymour Cray designed his first 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. Prior to the development of CRT system consoles, some computers such as the IBM 1620 had console typewriters.

Early microcomputers such as the 1975 Altair 8800 also relied on front panels, but since the introduction of the Apple II in June 1977, the vast majority of micros came with keyboards and connections for TV screens or other monitors.