It has long been the case that computer systems can signal serious faults using a series of beeps or flashes, where such faults occur too early in the boot process for them to be communicated in more conventional form.

There is a long history of this: modern PCs' motherboards can beep or flash their errors, and going back to 1986 the Sun 3/50 could indicate serious faults with the set of LEDs on its back panel.

What was the first system to use such a method? I'm interested in systems which had some kind of text interface as well; I'm aware that systems with only lights and switches could do little else.

  • I don't know the answer for a fact, only what I've encountered, so I'm entering it as a comment. The first computer that I've ever had that had beep codes for diagnostics (like no keyboard, no video, etc.) was my first original IBM PC. I'd had several other kinds of computers before that starting with the TRS-80 and don't remember any of the others having that feature. Commented Jun 8, 2017 at 14:57
  • @BillHileman Did any of those earlier systems of yours have easily removable graphics, RAM, etc.? I'd have to look to be sure, but I doubt that the IBM PC used beep codes for "no keyboard"; that's easy enough to display on the screen, and far friendlier to the user than an obscure beep code!
    – user
    Commented Jun 8, 2017 at 15:16
  • @MichaelKjörling I'm not 100% certain, but I do seem to recall it beeping if the keyboard was not attached, or not working. As far as easily-removed items, no. graphics and RAM were on PCI cards (I think that's what they were called?) but in the case of RAM and other plug-ins, the cards usually had DIP switches and jumpers for configuration. I don't think the beep diagnostics worked for any PCI cards, but there might have been a beep sequence indicating the motherboard or PCI bus was malfunctioning. Commented Jun 8, 2017 at 15:22
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    ASCII X07 is called BEL for a reason: on teletypes it rang a bell. A real electromechanical bell. Remember that typewriters always had a bell so the typist knew it was time to do a carriage return (by pulling a lever). And if the bell was there, it could be used. As far as I can recollected, beeps started replacing bells in the early 1980s. Commented Jun 8, 2017 at 15:46
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    @MichaelKjörling PC BIOS beep codes go all the way back to the original IBM PC model 5150. minuszerodegrees.net/5150/post/… It wasn't known as a particularly user friendly machine.Virtually everything was on an ISA card on the original IBM PC, video, floppy disk controller, serial and parallel ports. The CPU, RAM and keyboard controller were on the motherboard, but the RAM was socketted so that could be missing (or just not working properly) as well.
    – user722
    Commented Jun 8, 2017 at 16:46

2 Answers 2


Going back to mainframes which had wide words and large panels of indicator lights, it was possible to display messages on CPU registers quite comfortably. For example, on BESM-6 the boot-up error messages, like "NO BT DSK" or "DISK ERR", but in Russian, of course, were displayed using data cache registers consisting of 8 48-bit words (the second shelf from the bottom of the leftmost rack, with a large whitish rectangle of neon lights in the picture below). An OS even used scrolling to accommodate messages of arbitrary length.


That said, the question effectively asks "What was the first system with too few lights on the front panel to write letters or to scroll dots and dashes?"


The Harwell Dekatron, which is the oldest computer still in working order, has lights on its main control panel to indicate whether it completed its program successfully or halted due to an error. (If it was still running, you would hear the relays clicking and/or the very loud tape reader.)

Its main output was either by punching a paper tape or printing on a modified teletype. I don't think it could print text, only numbers.

An unusual feature of the machine was that you could also read the contents of main memory and the arithmetic accumulator directly by eye, due to the ionisation path maintained by the Dekatron tubes. This must have been a great help for troubleshooting.

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