# The apparently random blinking lights on old computers **URL:** \ **Category:** Factual Questions\ **Created:** [April 28, 2009, 3:33am UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587 "2009-04-28T03:33:56Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [April 28, 2009, 1:46pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/21 "2009-04-28T13:46:18Z")
> [@Mijin](#): > > Star Trek has lots of them too. > Even Data’s brain features cheery christmas lights. If he had room for a few banks of reel-to-reel tape machines and a punched-paper-tape output device, they’d be in there too. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 28, 2009, 2:17pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/22 "2009-04-28T14:17:25Z")
The version I knew was > [@](#): > > Alles Lookenspeepers! > > Das Komputermaschine ist nicht für gefingerpoken und mittengrabben. Ist easy schnappen der Springewerk, blowenfusen, und poppencorken mit Spittzensparken. Ist nicht für gewerken by das Dummkopfen. Das rubbernecken Sightseeren keepen Hands in das Pockets–relaxen und watchen das Blinkenlights. In other words, notice to visitors, you can look but don’t touch. I am amused that someone would think a machine wprth millions would have blinking lights just for show. - “Hey, the customer is paying millions for this machine and expects something more than a boring big metal rack. Let’s put some blinking lights! The customer will like that!”. - But this computer is for the Pentagon to calculate nuclear explosions. - So much the better. The military just love blinking lights. They will choose our IBM over Univac mainly because it has more blinkinglights, and in two colors! No contest!. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 28, 2009, 2:30pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/23 "2009-04-28T14:30:45Z")
> [@sailor](#): > > 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. No, I’m not wrong. I was specifically talking about the photo referenced in the quoted post. The photo is of a (relatively) modern computer - a Connection Machine from the '90s. The lights on it are for decoration. As I said in my post, they _could_ have been used for troubleshooting, but were unnecessary for the operation of the machine: [http://blogs.discovermagazine.com/sciencenotfiction/tag/connection-machine/](http://blogs.discovermagazine.com/sciencenotfiction/tag/connection-machine/) Next time. please read the entire post before responding. ---
**Author:** ![ethelbert](https://avatars.discourse-cdn.com/v4/letter/e/958977/32.png) [@ethelbert](https://boards.straightdope.com/u/ethelbert)\ **Post date:** [April 28, 2009, 2:42pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/24 "2009-04-28T14:42:44Z")
My favorite Hollywood computer was the one in [Desk Set](http://www.imdb.com/media/rm190355456/tt0050307). Lotsa blinkenlights, and, if I am not mistaken, the tape drives had no tape & spun in opposite directions. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 28, 2009, 2:42pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/25 "2009-04-28T14:42:57Z")
> [@beowulff](#): > > No, I’m not wrong. > > I was specifically talking about the photo referenced in the quoted post. > The photo is of a (relatively) modern computer - a Connection Machine from the '90s. The lights on it are for decoration. As I said in my post, they _could_ have been used for troubleshooting, but were unnecessary for the operation of the machine: [http://blogs.discovermagazine.com/sciencenotfiction/tag/connection-machine/](http://blogs.discovermagazine.com/sciencenotfiction/tag/connection-machine/) > > Next time. please read the entire post before responding. Yes, you were wrong. The lights indicated the state of the registers and _were_ used in actual operation. Plenty of evidence has been shown of this. The photos show they were labeled with the different register names. It has already been explained what they were used for. The OP was asking a general question. The fact that you can find an instance where a modern computer has lights which are less used or useful does not change the general fact that the lights were used and necessary. ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [April 28, 2009, 2:58pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/26 "2009-04-28T14:58:48Z")
Old days aren’t so far away. On my networking shelf, I have a router, switch, print server, modem, and phone adapter, all with blinking lights. Very retro at night. Most of the time they mean nothing, just a hypnotic background visual, but if something went wrong (i.e., cable is down) or I have a question (connection speed of a device) they come in handy. Now, if we can get to the origin of the machine that goes _bing_… ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 28, 2009, 3:02pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/27 "2009-04-28T15:02:29Z")
> [@sailor](#): > > Yes, you were wrong. The lights indicated the state of the registers and _were_ used in actual operation. Plenty of evidence has been shown of this. The photos show they were labeled with the different register names. It has already been explained what they were used for. The OP was asking a general question. The fact that you can find an instance where a modern computer has lights which are less used or useful does not change the general fact that the lights were used and necessary. Maybe I need to make my posts simpler for you. I’ll try to write in smaller words - when I wrote “Those” I specifically meant the lights on the Connection Machine in the photo. I worked I on DG [Nova](http://ed-thelen.org/comp-hist/dg-nova.jpg), so I am well aware of what the indicator lights are for on old machines. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [April 28, 2009, 3:04pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/28 "2009-04-28T15:04:50Z")
> [@Mijin](#): > > Star Trek has lots of them too. > Even Data’s brain features cheery christmas lights. Yup. Here’s Data’s noggin: [http://images1.wikia.nocookie.net/memoryalpha/en/images/7/78/Positronicbrain.jpg](http://images1.wikia.nocookie.net/memoryalpha/en/images/7/78/Positronicbrain.jpg) Now, behold the M-5 multitronic computer: [http://images2.wikia.nocookie.net/memoryalpha/en/images/3/3e/M-5.jpg](http://images2.wikia.nocookie.net/memoryalpha/en/images/3/3e/M-5.jpg) The suspiciously similar Atavachron: [http://images4.wikia.nocookie.net/memoryalpha/en/images/0/03/Atavachron.jpg](http://images4.wikia.nocookie.net/memoryalpha/en/images/0/03/Atavachron.jpg) Which looks a whole lot like Gary Seven’s Beta 5 computer: [http://images1.wikia.nocookie.net/memoryalpha/en/images/4/4b/Beta5Computer.jpg](http://images1.wikia.nocookie.net/memoryalpha/en/images/4/4b/Beta5Computer.jpg) One might take this as proof that some computer company is going to be as dominant in Kirk’s time as Microsoft is in ours. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [April 28, 2009, 5:50pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/29 "2009-04-28T17:50:15Z")
Another old-timer from the PDP-11 era. I did indeed use the lights to see how things were going. It was sometimes possible to tell if the\* program was in an infinite loop or just taking a long time by looking at the lights. Then I’d stop the program and use a switch to step thru the loop to determine what it was doing. I can still look at network gear and detect unusual activity by a quick glance at the lights. \*of course it was “the” program. These things only ran one program at a time. ---
**Author:** ![busterpickle](https://avatars.discourse-cdn.com/v4/letter/b/258eb7/32.png) [@busterpickle](https://boards.straightdope.com/u/busterpickle)\ **Post date:** [April 28, 2009, 7:01pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/30 "2009-04-28T19:01:13Z")
I thought the turbo light was also for accuracy. I believe it dropped the speed down to 8MHz and some programs were written to compensate for the inaccuracy in calculations that the 8MHz processor made. Or, something like that. I remember in Pascal class in high school (circa 1992) we wrote a program that compensated for the 8MHz processor for large calculations. Any ways, as far as blinky lights go, I dragged out this rack mount, modular, modem chassis from UMD many a year ago. It consisted of many 2400 baud modems that were in cards. When you turned it on it did this fantastic boot sequence where they all cycled up and the lights lit up and scrolled and the occasional random lights would flicker from time to time. We called the machine the BLM-14/2400. Which stood for “Blinky Light Machine” and the 14/2400 was for the 14, 2400 baud modems. We had a friend fooled for months thinking it stood for balanced-line-monitor or whatever. We even made fake excel data for him as well. It was great. 🙂 eb ---
**Author:** ![DanBlather](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@DanBlather](https://boards.straightdope.com/u/DanBlather)\ **Post date:** [April 28, 2009, 7:32pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/31 "2009-04-28T19:32:26Z")
> [@beowulff](#): > > No, I’m not wrong. > > I was specifically talking about the photo referenced in the quoted post. > The photo is of a (relatively) modern computer - a Connection Machine from the '90s. The lights on it are for decoration. As I said in my post, they _could_ have been used for troubleshooting, but were unnecessary for the operation of the machine: [http://blogs.discovermagazine.com/sciencenotfiction/tag/connection-machine/](http://blogs.discovermagazine.com/sciencenotfiction/tag/connection-machine/) > > Next time. please read the entire post before responding. The lights on the Connection Machne did serve the purpose of diagnostics/performance tuning, but they also had a mode that would flash them randomly to look more interesting. When you have a multi-million dollar machine it is sometimes necessary to make it look cool to the folks that authorize the money to buy it. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [April 28, 2009, 7:52pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/32 "2009-04-28T19:52:30Z")
Correction: “When you have a multi-million dollar machine it is [del]sometimes[/del] **always** necessary to make it look cool to the folks that authorize the money to buy it.” Stranger ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [April 28, 2009, 7:59pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/33 "2009-04-28T19:59:58Z")
> [@DanBlather](#): > > When you have a multi-million dollar machine it is sometimes necessary to make it look cool to the folks that authorize the money to buy it. But does it go “_ping!_”? ---
**Author:** ![redtail23](https://avatars.discourse-cdn.com/v4/letter/r/3e96dc/32.png) [@redtail23](https://boards.straightdope.com/u/redtail23)\ **Post date:** [April 28, 2009, 8:00pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/34 "2009-04-28T20:00:42Z")
You’re both right, so quitcher bitchen. Yes, old computers had useful lights that were actually used by programmers (to read registers, etc.). Yes, modern computers have useful lights that are actually used on occasion (connection lights, etc.) but that most people ignore most of the time. However, a few years back I was at a small technical seminar given by the head of a giant, new, multi-gazillion-dollar lab that had been set up. Spiffy new lab had a glassed-in data center for their servers. Servers in the lab had all been turned around with the backs faced to the glass…so that the VIPs on tour would get to see blinky lights, because otherwise the deep pockets didn’t feel like they were getting their money’s worth. I can’t find the links now, but you can buy panels of just blinky lights, purely for effect. In fact, there’s a guy that sells blinky light & fake knob panels for music studios, for much the same reason. Some of the testimonials on his site are hilarious. ---
**Author:** ![gazpacho](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@gazpacho](https://boards.straightdope.com/u/gazpacho)\ **Post date:** [April 28, 2009, 8:19pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/35 "2009-04-28T20:19:52Z")
I develop hardware for embedded computer systems. Unlabeled blinkenlights are actually still very useful in this day and age. We have prototype boards for phones and they almost always have blinkenlights and various places in the software to run the phones the software will put out a specific pattern. This is basically like a print statement in a program running in the terminal. We can see what the software is doing. What the lights mean varies with what we are trying to debug. Usually we get past the blinkenlights stage pretty quickly and have useful messages sent over a USB link but for initial debug they are of great benefit. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [April 28, 2009, 9:49pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/36 "2009-04-28T21:49:46Z")
> [@electronbee](#): > > I thought the turbo light was also for accuracy. I believe it dropped the speed down to 8MHz and some programs were written to compensate for the inaccuracy in calculations that the 8MHz processor made. If a CPU was inaccurate at a certain speed, it would _never_ be run at that speed in any kind of factory-default setting. This is why overclockers\* like early revisions of any new CPU design: The factory doesn’t know what the precise limits of the design are, so they’re overly-conservative and default to only shipping machines that will run the CPU at a relatively low speed that they’re willing to guarantee. \*(People who run CPUs at an unusually fast speed regardless of what the company is willing to guarantee. _For fun_, usually.) The above doesn’t take into account things like the [Pentium FDIV bug](http://en.wikipedia.org/wiki/Pentium_FDIV_bug), which only occurred in one opcode, or the [Pentium F00F bug](http://en.wikipedia.org/wiki/F00f) or the [Cyrix ‘coma’ bug](http://en.wikipedia.org/wiki/Cyrix_coma_bug), which were rather subtle design flaws relying on the vagaries of uninterruptable states and pipelining. All of those bugs would have happened at any speed before the silicon began to melt. It’s possible to have bad RAM, though, which might only mainfest when you do RAM-intensive tasks. A number of early Linux enthusiasts were stymied by [SIG11 errors from gcc when they tried to compile the kernel](http://www.bitwizard.nl/sig11/) due to bad RAM their crappy BIOSes would pass without a complaint. I haven’t heard of anyone getting bitten by bad RAM in a long time, though. This, again, would likely not be speed-dependent, AFAIK. ---
**Author:** ![FORTRAN\_forever](https://avatars.discourse-cdn.com/v4/letter/f/f17d59/32.png) [@FORTRAN\_forever](https://boards.straightdope.com/u/FORTRAN_forever)\ **Post date:** [April 28, 2009, 9:52pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/37 "2009-04-28T21:52:03Z")
> [@gazpacho](#): > > We can see what the software is doing. Back in the good old days there were two “the blinking lights are no longer blinking” scenarios that would drive a spike of fear into my programming heart. 1. The lights were no longer blinking, but in a non-changing pattern with different lights shining at different intensities. That meant that my program was stuck in a loop (the lights were still technically blinking, but each light was going on and off in a steady pattern that caused human eyes to see it as shining steadily in a partially-lit state). 2. Each light was either solid on or solid off. “He’s dead, Jim.” ---
**Author:** ![DocCathode](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doccathode/32/18773_2.png) [@DocCathode](https://boards.straightdope.com/u/DocCathode)\ **Post date:** [April 28, 2009, 10:08pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/38 "2009-04-28T22:08:27Z")
My late father used to proudly tell the story of how he compiled a program to play tic tac toe with the blinkenlights on the office machine. It became quite popular in the office. I miss Dad. ---
**Author:** ![Shawn1767](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@Shawn1767](https://boards.straightdope.com/u/Shawn1767)\ **Post date:** [April 28, 2009, 11:06pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/39 "2009-04-28T23:06:58Z")
Thanks for all the responses so far. However, I don’t know if I am any closer to understanding how they convey information. I mean, I have a DSL modem and there are blinking lights on it, but those are LABELED and if one isn’t blinking, I know I don’t have a connection or something. And in some of the pictures you guys have posted it shows one row of lights and some look to be labeled somehow. However, if you look in this picture: [File:Frostburg.jpg - Wikipedia](http://en.wikipedia.org/wiki/File:Frostburg.jpg) I mean, how do you just look and say, “Oh, the red light 36 rows down and in the 5th column isn’t blinking right, Frammer number 6 must not be working correctly.” I mean, if there were linear rows of lights and the longer the row lit up, then maybe I could get some information out of it, but I mean, yeah, when you see a bunch of red lights and you say “Oh, the pattern’s not right,” how do you KNOW the pattern’s not right? And if it’s not working when the blinking lights are no longer blinking, couldn’t you just get away with one light then? Thanks. ---
**Author:** ![DanBlather](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@DanBlather](https://boards.straightdope.com/u/DanBlather)\ **Post date:** [April 28, 2009, 11:20pm UTC](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587/40 "2009-04-28T23:20:06Z")
> [@Shawn1767](#): > > Thanks for all the responses so far. However, I don’t know if I am any closer to understanding how they convey information. I mean, I have a DSL modem and there are blinking lights on it, but those are LABELED and if one isn’t blinking, I know I don’t have a connection or something. And in some of the pictures you guys have posted it shows one row of lights and some look to be labeled somehow. However, if you look in this picture: [File:Frostburg.jpg - Wikipedia](http://en.wikipedia.org/wiki/File:Frostburg.jpg) > I mean, how do you just look and say, “Oh, the red light 36 rows down and in the 5th column isn’t blinking right, Frammer number 6 must not be working correctly.” > I mean, if there were linear rows of lights and the longer the row lit up, then maybe I could get some information out of it, but I mean, yeah, when you see a bunch of red lights and you say “Oh, the pattern’s not right,” how do you KNOW the pattern’s not right? And if it’s not working when the blinking lights are no longer blinking, couldn’t you just get away with one light then? > > Thanks. One of the machines I worked on displayed the binary value of the registers as well as the program counter (i.e., the address of the code currently being executed). If the machine halted because of an error you could see where in the code it was as well as the operands’ values. You could also often “single step” old computers instruction by instruction to see what was happening. [Previous page](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587.md?page=1) [Next page](https://boards.straightdope.com/t/the-apparently-random-blinking-lights-on-old-computers/494587.md?page=3)