The apparently random blinking lights on old computers

I wondered this a long time ago and here’s an example: In “Wargames” there is a military computer called “WOPPER” or something like that. Anyway, all along its sides are rows of lights that go off and on seemingly at random. I think they also had something like this on the original Star Trek series.

Were there computers or displays like that that just had random lights? How could they convey information? What was their purpose?

Or is it all just Hollywood trying to look cool, but not really thinking about how or why lights would do that?

It’s Hollywood trying to look cool.

Not true. Many early computers had blinkenlights. The first hobbyist computer, the Altair 8800 System did, as did various IBM systems. They didn’t have as many as the Hollywood versions, but the Connection Machine had plenty.

Yep, I’m grizzled.

Sorry, Sunspace, but I just found this:

Again, how did they tell what the red lights meant? It would seem to be difficult if they weren’t labeled or if you had to know what the right pattern was.

This has at least some foundation in fact: Computers used to have front panels, which did indeed feature lights and switches and sometimes dials, which allowed people to operate the computer without any software being loaded on it (this was commonly done to bootstrap the machine, where each time the machine was turned on a small bootloader program would have to be toggled in on the front panel), or to debug software without having to load an additional debugger. It also let people control more mundane things like which tape drive or disk pack the computer would try to boot from.

Even the random flashing has a basis in fact: RSTS/E, an OS for DEC’s PDP-11, had a Blinkenlights mode which would blink the front panel’s lights in a recognizable pattern when the machine was otherwise idle.

In principle, you could do anything the machine was capable of doing simply from the front panel: Use the switches to toggle in software and data and use the lights to read the state of memory after a program run to get your results. In practice, this was horribly tedious and all computers ever to see serious or semi-serious usage grew better input-output facilities.

This page shows a lot of different styles of front panel, from companies as diverse as DEC, Hewlett-Packard, and IBM.

They were labelled, and the people around them would have enough knowledge of the hardware to make sense of various patterns. In those days, even getting near a computer implied a certain degree of technical knowledge or, possibly, a rabid desire to acquire such knowledge.


ACHTUNG! Alles touristen und non-technischen peepers!

Das machine control is nicht fur gerfinger-poken und mittengrabben. Oderwise is easy schnappen der springenwerk, blowen fuse, und poppencorken mit spitzensparken.

Der machine is diggen by experten only. Is nicht fur geverken by das dummkopfen. Das rubbernecken sightseenen keepen das cotten picken hands in das pockets, so relaxen und watchen das blinkenlights.
More seriously, some of those old scifi looking mainframes were, in fact, used as props in movies after they became obsolete.

The Altair wasn’t the first hobbyist computer. Depending on how you figure ‘hobbyist’ and ‘computer’, you can come up with various models, but the Boston Computer Museum judged in 1987 that the Kenbak-1 was the first commercially-available personal computer. It was first sold in September, 1971, and it did indeed have a front panel.

I suspect that those lights were mostly for decoration. They may have been useful for troubleshooting faulty hardware, but they weren’t used for the actual operation of the machine.

Here’s a few photos of even earlier computer consoles. You will note that the lights are labeled:

A lot of specialty computer systems used in movies are actually surplus computers. For instance, in the movie *Eve of Destruction* (yeah, I’ve never heard of it either) part of an IBM AN/FSQ-7 from the Semi-Automatic Ground Environment detection and control system was used. Although it looks pretty dated, even for 1991, apparently the set designers thought it looked futuristic. Actually, this one seems to have gotten around like the cheerleading squad, as has the DEC PDP series. The “W.O.P.R.” console used in WarGames (which, according to Wikipedia stands for “War Operation Plan Response”) is just a prop; however, a IMSAI 8080 used by Broderick was the real thing, if about as powerful as a calculator wristwatch.

As for the purpose of the blinking lights, believe it or not back before the day of multifunctional display terminal, window paging systems, Graphic User Interfaces, et cetera a lot of diagnostic and functional information could be read from the diagnostic (flashy light or “blinkenlight”) console. Of course, this is back in the day when programmers would spend days fiddling with the data write sequence to make retrieval faster. You could still program a computer to output analog signals to write to a light console; see the BeBox and the Connection Machine both had panels of blinkenlights, albeit more for geek catchet than any practical purpose. In Neil Stephenson’s Cryptonomicon, the main protagonist uses the power light for data output as he is concerned about his captors gaining screen output via Van Eck phreaking (though this is unlikely; more likely they’d install some kind of bit-grabber between the keyboard and systemboard, or a resident Trojan).

However, here is something even cooler than an old computer with a big blinkenlight console. When I was in school I worked in one of the oldest buildings on campus and we went up to the attic one day to pull out some tables only to find something like this (but smaller) under covers. Unfortunately, we didn’t have a plotter, but someone managed to connect it to ADC board and we got it cleaned up and working with a drill motor powering it. Nerdy-cool stuff; we plotted ballistic traces and computed compound decay rates with it until somebody got wise and took it “for the museum” that was never built.


Aha. Found what I was looking for. Here’s a page about an old USAF computer console that’s been used as a prop in movies from the 1960s. Just about any cheesy scifi show you can think of, it’s been there. Lost in Space, Battlestar Galactica, Independence Day, Lost…

More than any other, that’s the iconic Big Wall of Computer with Lots of Blinkenlights.

ETA: Man, this crowd is on top of the obsolete computers :wink:

Given that SAGE was designed in the 1950s to shoot down Russkie bombers, I wouldn’t guess it looked dated by 1991. :wink:

Not surprising: The PDP-8 in particular sold like hotcakes, especially since it was within the purchasing power of middle management in the 1960s. For once each division of a company could have its own computer!

I forgot to mention something that was on some early front panels: A CRT (Cathode Ray Tube, the big glass tube in old TVs and computer monitors) screen that mirrored the contents of the CRT you were using for RAM as part of a Williams tube. The display end of the CRT actually in the Williams tube had to be covered by a charged metal plate to be of any use, but you could paint two CRTs with the same data (charge pattern), one of them being built into the front panel. The upshot was that you could look over and see what was in RAM by reading the CRT. The Manchester Small-Scale Experimental Machine (a.k.a. The Baby) used this design in the late 1940s; it was the first stored-program computer, meaning it’s the first computer in the fully modern sense of the word.

You guys aren’t looking back far enough!

Blinking lights on real-world computers go back to essentially the very first electronic computer, ENIAC:

Based on the publicity this and other really early computers (like UNIVAC) got, Hollywood put apparently random flashing lights on all their fake computers throughout the 1950s, '60s, '70s, and '80s.

Have you looked at a cable modem and router lately? I’m sitting across a dark room from mine, and I can see from the blinking lights that the cable modem has an active internet connection, the router has a connection to the modem, which computers are connected to my network and when they’re sending or receiving data.

Remember that idiotic TV show “Voyage to the Bottom of the Sea”? The sub had a whole wall of blinking lights…that seemed to be always flashing. apparently, Admiral Nelson could figure out what the display meant (it usually was signalling that a foam-rubber monste had gotten aboard). I’m sure that thing wa used in seeral movies as well.

You suspect wrong. As can be seen in many of the links already supplied, the lights represented bits in the different registers and memory locations which could be set (programmed) using those switches and lights.

Unlike today, the machine had NO bootstrap program or standard initial location so, to start the machine you would do something like this:

  • Load the bootstrap program into memory bit by bit and word by word into memory using the switches and lights. This took time and mistakes were easily made so it had to be double checked.
  • Similarly load the address of the first instruction of the bootstrap program into the instruction address register and any other necessry values into other registers. No blinking lights up to this point.
  • Once everything was programmed you flipped the “RUN” switch and, if everything went well the bootstrap program would load the actual program to be run from whatever peripheral, often paper tape or cards. Very often things went wrong and stopping the running of the computer allowed to check values in registers and memory. The lights only blinked fast while the computer was running and the values in registers changed rapidly. While the operator was checking or programming the machine was not running and the lights were not blinking.

All this becamen gradually unnecessary because bootstrap programs were hardwired and you had no choice as to where it was located in memory. For example, on start the computer would automatically go to the highest or lwest memory position and get the address of the first instruction from there.


Star Trek has lots of them too.
Even Data’s brain features cheery christmas lights.

My ancient and venerable IBM PS2 had not just lights that blinked for no particular reason, but also a “Turbo” button that did nothing I could determine.

The “Turbo” button on PS/2 computers (and other computers of that era) was actually a “slow down” button labeled in reverse. The idea was that if you had an older piece of software that didn’t use the PC’s timer chip for timing, and therefore ran faster on a faster computer, you could slow it down by hitting the “Turbo” button. This was useful for some games, since on a faster computer things would just whiz by so fast you couldn’t control anything and you would crash your plane/racecar/whatever.

If you didn’t notice any difference between “Turbo” (normal) mode and the slow mode, then you weren’t using any software that put a heavy load on the CPU.

The only blinkenlight I remember on a PS/2 was the hard drive access light.