Debugging A 1950s Computer Sounds Like A Pain

Debugging computers in the 1950s sounds like it wasn’t an easy task. That’s one of the interesting facts from this fascinating talk by [Guy Fedorkow] about the Whirlwind, one of the first digital computers ever built. The development of this remarkable computer started at MIT (Funded by the US Navy) in 1949 as a flight simulator but pivoted to plotting interceptions in the early 1950s. That was because the USSR had just set off their first boosted nuclear bomb, which could be mounted on a missile or bomber. So, the threat of incoming missiles and atomic bombers became real, and the need arose to intercept nuclear bombers.

As a real-time computer, Whirlwind received radar data from radar stations around the US that showed the location of the interceptor and the incoming bogey, then calculated the vector for the two to meet up and, erm, have a frank exchange of views. So, how do you debug one of the first real-time computers? Carefully, it seems.

The GUI aspect of the Whirlwind was a cathode ray tube (CRT) display and a light gun that could be used to select a spot on the screen. Point the gun at the screen, press the button, and the computer plotted the chosen spot. It could also be used more like a mouse: you could select a program to run by pointing the light gun at a menu of numbers on the screen. In its intended use, the operator would use the light gun to designate the interceptor and target. We’ve written more about the system (called Volscan) and how it evolved to be used in civilian air traffic control (ATC) systems here.

“While engaged in research problems involving extensive computation, Whirlwind computer, a portion of which is shown below, enhances the educational program at M.I.T.” From the MIT Museum.

Amusingly, [Guy Fedorkow] describes how the builders of Whirlwind got a local furniture maker to build the cabinet for the CRT, only to realize that their navy paymasters would hit the ceiling if they realized that they had spent money on making the cabinet look nice. So, they painted it battleship grey and hoped they would not notice. The Navy had cause to be concerned: Whirlwind was consuming nearly eighty percent of the budget of the US Navy research office, according to [Federokow].

The Whirlwind was not a complex computer, though: it was a 16-bit computer with only 2048 words of memory. It could handle just 50,000 add functions a second. Compare that to a Raspberry Pi 5, which can handle over 10 GFLOPS. The Whirlwind also consumed an incredible 100 kilowatts of power to perform this arduous computer task, while the Pi 5 needs about 12 watts. The Whirlwind didn’t support floating point maths, so it used several shortcuts to calculate the vector for the interceptor that approximated the trigonometric maths needed.

Remember that this is working in real-time, using actual radar data. That didn’t leave enough space for breakpoints or logging. So, [Fedorkow] thinks that they used pre-arranged problems and good planning to debug the system: they

“…didn’t just sit down and write the code and throw it on the machine. There are reports of all kinds of experiments and modules done to test pieces of the algorithm independently. So when they did assemble the whole thing, they probably knew how most of the pieces worked already…. In fact one of the young Frank Heart’s projects was to figure out how to “play back” the radar tapes onto 16mm film, I assume so they could see what the radar station would have been saying while the data was being replayed into Whirlwind. I think he tried several off-line tricks to try to get it to work with just the analog gear, but it seems ultimately he gave up and wrote WW code to drive a display. ” 

(from the article notes (PDF link) to the  article Recovering Software For the Whirlwind Computer)

From the MIT Museum

The engineers broke the problem into parts and hand-calculated how the algorithm would interpret certain data sets. They then “ran” each part by calculating the results by hand, simulating the computer on paper. They did this because they only got access to the computer for about 12 hours a week, and they needed to ensure they got the most out of this time.

The Whirlwind project ran until 1959 when it was decommissioned and broken up into parts, replaced by the next wave of digital computers that offered much more computing power without the need to fill an entire basement for the power supply alone.

Thanks for the tip, [Stephen Walters]!



24 thoughts on “Debugging A 1950s Computer Sounds Like A Pain

  1. Impressive. Reading this I realize there was something positive about the cold war era, also, I think. People were worried about an uncertain future, worried about a n*clear war and tried to enjoy their present life as best as possible, rather than talking about jobs and money all the time. Those people saw purpose in their life and work, also by trying to preserve peace and/or prevent a catastrophe. All that pressure wasn’t healthy for sure, though it also posed a challenge. The circumstances made people think. Think about consequences and about things that mattered. Maybe that’s why people back then were more profound, maybe and why there were such ingenious inventions being made at the time. Or maybe I’m wrong. This was long before my time, after all.

    1. It only went on pause for about 30 years and here it comes again. If you are young enough not to have experienced the first round.. don’t worry you are plenty young enough to experience the second.

    2. I’m not happy to see the danger of World War and especially Nuclear War coming around again but if it does mean people will be looking towards big things and the future rather than being lost in the mental fog of whatever is going on with their favorite reality TV celebs and pretending to be rich going in to debt to buy ridiculously expensive cars and iPhones… that’s one hell of a silver lining!

      The social progress that has been made is good but the rest of this shallow, eye-of-the-storm between conflicts culture we have developed really sucks.

      1. Be aware that constantly being on top of hacker/tech news, and buying the greatest ever 2,5G router or premium refurbished Amiga can be the same behavior. At least, when you are only consuming, and not tinkering yourself.

    3. That kind of optimism is something that’s been taken away from the younger generation. The ones that reject talking about jobs and money to instead live in the moment are the consumers that are immersed in social media and whatever the latest films and celebrity news are. The ones who are trying to prevent a catastrophe are the ones who are talking about the cost of living versus the price of labor, about the bad signs in the economy, about the climate, about disease, war, famine, etc.

      Do you expect them to smile while they look around and realize all the things they were promised as kids are getting further and further away the harder and longer they work. Let me set a scene. Imagine retiring in good health and no debt to live in a house like the one you grew up in, and looking up from your gardening to see your kids arrive for a visit with their families. Imagine that you decide to take everyone to the local lake to fish, or to treat everyone to steak at the local mom&pop restaurant. If you’re young and not uncommonly lucky, then unless you dedicate your life to chasing that goal, you’ll never come close. Even if you do manage to buy a house, which will probably be as old and in worse shape than the one you grew up in, you’ll have a hard time growing much in the garden, what fish there still are may not be good to eat, and the steak will be too expensive. That’s how the future looks to a young person who isn’t living in the moment, in my opinion.

    4. It was before their homes were turned into economic zones and all global cultures were thrown into an Americanizing blender to make money flow more easily. They did feel more purpose and meaning in life, yes.

  2. If you follow the MIT Museum link below the photo and scroll down a bit there is a different view. The dark bezzel around the CRT hinges up to reveal 10 controls (I was unable to find a link that did not grey-out the photo!).

  3. Groundbreaking machines in many ways.

    From Whirlwind to MITRE: The Story of The SAGE Air Defense Computer (History of Computing)
    MIT Press – October 16, 2000
    547 pages

    SAGE bears comparison with Manhattan Project, the Atlas and Polaris missile programs, and the Apollo moon program. As one of the great technological and managerial achievements of the Cold War, it has long deserved the history that Redmond and Smith have now produced. ― Alex Roland, Duke University

  4. I’m just wondering what they did with the bugs after they had found them ….. put them in a jar for deterring other bugs from getting into the machine … or feed them to an iguana or other bug eating animal?

  5. The development of Whirlwind was an amazing story in itself. The professors at MIT had some highly innovative ideas on how to run a government project.

    For instance, they started buying parts immediately, *before* the design was done! The Navy was flabbergasted by the huge early expenditures, and so tried to cut off funding. But by the time it could act, Whirlwind had already bought all the parts.

    They then proceeded to design the computer around the parts they had. By deliberately limiting their component options, they forced the designers to innovate and focus on getting the job done with “good enough” solutions, rather than waste time seeking the “ideal” part or “perfect” circuit.

    They also set up parallel paths to invent solutions for problems where the desired parts didn’t exist (such as the memory and display).

  6. “The Dream Machine” is a book on Licklider

    I did a great deal of research on Whirlwind as software curator at the Computer History Museum, and did the recovery of the paper tapes and magtapes. Most is available on

    Whirlwind was not destroyed in 1959. Bill Wolf rebuilt it and used it at his company Wolf Research into th e 1970s. When it was finally scrapped, Ken Olsen of DEC saved the pieces that now are preserved at CHM. Bill Wolf donated the collection of paper tapes and magtapes later, where they had been saved in a basement.

  7. Whirlwind was the progenitor to SAGE, Semi Automatic Ground Environment. SAGE comprised the efforts of MIT, IBM, Burroughs, AT&T, Western Electric, Software Development Corporation (SDC] and a number of other contractors. SAGE was pretty much obsolete by the time it was partially deployed in the early 1960s. Still, many technical developments which were incorporated into SAGE arguably jump started many military and civilian applications we still use. There are a number of films about SAGE which have been uploaded to YouTube and and very interesting to watch in the context of the 1960s and also now. One of the slicker films is by SDC which explains how simulation data were complied to exercise the system and train the staff. The sheer vastness of the SAGE system is impressive, especially considering it had to be developed from the technology of the late 1950s and early 1960s.

  8. In the mid ’70s I taught new operators for the SAGE system. SAGE’s AN-FSQ7 computer was the result that came out of the Whirlwind research.

    The Air Force couldn’t afford a SAGE system for training, so we trained on a BUIC system programed to act like SAGE. (The BUIC system was interesting in its own right.)

    The Q7 was a vacuum tube system with 68k of 32 bit core memory. For 20 years or so the Air Force tried to build a replacement but they were never reliable enough. The SAGE had nearly 100% redundancy and almost never went completely down. Of course that pretty much made them cost double.

    I believe the last was retired in 1983.

    I read about them, studied their instruction set, and taught people to use them. But I never got to see a Q7. And that makes me sad.

  9. Whirlwind marks the beginning of a new age, like the Industrial Revolution. It would be instructive to look at the blow-back from this technology, hypothesized climate change; and begin to think about the blow-back from the Whirlwind Revolution…….

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.