The Marvellous Analytical Engine- How It Works


Hi All! As promised: Babbage’s Analytical Engine, how the heck did it work?

If you’re new to this website, you may be only dimly aware of Charles Babbage’s marvellous yet mysterious Analytical Engine, the first design for a real computer, from the 1840s. It had programs, memory, cycles, loops, and all sorts of computery things despite being constructed entirely out of brass gears and powered by a steam engine. When I started this comic I was extremely frustrated by the vagueness of nearly every single description of it. Eventually I had to build my own,  in computer-generated form (how meta!). I found out that it’s not only a delightfully beautiful machine jam-packed with ingenious devices, it’s also considerably easier to understand than a modern computer. How the heck do those things work?

The Thrilling Adventures has an appendix with many diagrams and explanations of how the Analytical Engine worked and how it relates to modern computers, but I think despite the pleasures of print the broad operation of the Engine is most clearly explained by animation. I hope this video makes it clearer– I should stress that a) this is a super-simplified, cartoon, stripped-down version, and b) this is the best of my understanding, gleaned from the papers of the late Allan Bromely (lent to me by John Graham-Cumming, thanks John and I’m totally returning them I swear!!) who wrote I think the most complete modern descriptions of the Engine. I could be SO TOTALLY WRONG on a lot of stuff. So that said, here we go (I um and er a lot less after the first couple of minutes I promise…):

Historical note: I had a moment of sisterhood with Ada Lovelace when I was writing out how the Engine worked. In her correspondence with Babbage while writing her famous Notes on the Sketch of the Analytical Engine, there’s a little exchange between them that neatly displays their personalities. Babbage writes:

There is still one triffling misapprehension about the Variable cards—A Variable card may order any number of Variables to receive the same number upon theirs at the same instant of time—But a Variable card never can be directed to order more than one Variable to be given off at once because the mill could not receive it and the mechanism would not permit it. All this was impossible for you to know by intuition and the more I read your Notes the more surprised I am at them and regret not having earlier explored so rich a vein of the noblest metal.

To which Lovelace replies with the harassed tone familiar to someone buried under piles Analytical Engine diagrams:

I cannot imagine what you mean about the Variable-Cards; since I never either supposed in my own mind that one Variable-card could give off more than one Variable at a time; nor have (as far as I can make out) expressed such an idea in any passage whatsoever.

This is the sort of thing one glances blandly at when reading historical correspondence, until one finds oneself writing: “The Variable Cards then read off the numbers on the addresses into the Mill”.. and then scrupulously adding “ONE AT A TIME” as the ghost of Charles Babbage hovers anxiously over one’s shoulder…

Anyways if you are super keen on this stuff and want to see specifics of some of the thousands of little levers, here is the video on the anticipating carriage for carrying the ones (that still by the way leaves out some bits). Babbage would be beside himself with delight that the first question asked a talk I gave on the comic at Google was how he planned to carry the ones! This part of the Engine was Babbage’s proudest achievement, he called it ‘teaching the Engine to foresee, and to act on that foresight’.

(I have a few more videos on the Engine on YouTube, though they have less explanation, which you may consider a feature.)


Get your lovely hot Analytical Engine prints!


ALSO- by popular demand, you can now buy prints of the Analytical Engine visualisation in glorious Technicolor! (a previous post explained why the colours I chose to paint the Engine are so.. festive). I have some new tshirt designs and a couple of more prints on the way, as soon as I have a half a second which I currently don’t.

Many are asking, will there be more Lovelace and Babbage? The answer is YES! But you’ll have to hold on a YET couple of more months. As some of you may know, I am only a fearless comic-drawer by night; by day I battle giant monsters in the glamorous yet terrifying colosseum of visual effects animation.

In the meantime you can feast your eyes and ears on my flyaway hair and become thoroughly sick of my insufferable squeaky voice on several interviews (not a complete list.. more to come!), legacy of my Book Tour of Doom which I must tell you all about sometime when I have a sec. Also, I’m relieved to report that after being braced for brickbats and jeering if not total baffled silence, there’s a whole bunch of great reviews out for The Thrilling Adventures of Lovelace and Babbagelinks to a bunch at the bottom of this page.

AND FINALLY.. if you are around London this coming weekend you can catch me at the Stoke Newington Literary Festival on the comics panel on Sunday.


  1. Jonathan W on September 17, 2015 at 8:42 pm

    Just heard you on a recording of BBC’s The Museum of Curiosity: Coding Special taking about this, Babbage and Lovelace. Just hope that one day will decypher Babbage’s flow charts and build it.

  2. Hugh on August 21, 2015 at 12:19 pm

    Just so you know, I did a blog posting about this book for the world-wide Association for Computing Machinery (ACM)’s Special Interest Group on Computer Science Education (SIGCSE), at : I greatly appreciate this book, and I enthusiastically recommend it to others.

  3. Natalie on July 29, 2015 at 1:53 am

    Hi Sydney,
    you might already know Lego are proposing an Ada Lovelace and Charles Babbage set;, Not as good looking as your creations but what fun to play with.
    Also congratulations on the book! It’s on my birthday wish list so hope yo get it soon.

  4. adrian ellis on July 1, 2015 at 8:58 pm

    Darn, DARN! I very much enjoyed your book (lovely illustrations!) and the above article is also jam-packed with excellent info and daunting technical doo-dahs, but Babbage choosing decimal? What a fool! Ah AH HAH HAH!… (cough). Where was I? Oh yes, the earlier DARN was caused by your ‘red rag to a bull / gauntlet thrown down’ comment in your article that stated: ‘a modern computer. How the heck do those things work?’ Being another Canadian born, London living, ‘trace-of-a-canadian-twang-that-got-me-laughed-at-in-primary-school’ accented, computer-nerdy, illustrating with vectors, personage, I feel that the challenge implicit in your above comment MUST BE MET! I will endeavour (no, I’m not going to change that to endeavor) to create an ANALOGY that represents the modern, digital computer in a vivid, clear, correct and meaningful way with illustrations whose charming simplicity carefully masks my endemic ineptitude. The ANALOGY will explain how the following elements work: CPU registers, memory, the OSI seven layer model (including TCP/IP specific session, packet control and hardware layers) and it will involve a Victorian factory (Nice!) but without the fumes, caustic gases and odd machine-severed fingers (Eurgh!). It’ll even have a virus. Ha HAH! The challenge has been ACCEPTED!*

    *Note: The project might take some time. Really, a lot of time. Updates will be posted on

  5. Scott on June 26, 2015 at 7:02 pm

    Sydney, just heard you on BBC Tech Tent. Great job! I know you think you have a “squeaky” voice, but I think it is a great voice for radio. Your frequencies are right in the sweet spot. When (not if) the B & L animated movie is produced, you should absolutely be Ada’s voice. I really liked your ‘dramatic’ reading. Not so much the fellow who did Babbage though. He sounded too much like a BBC announcer. I think maybe Eddie Izzard would do a good Babbage. He has the same kind of a frog mouth that Mr. B did.
    Also, you did really good off the cuff talking, even when they asked you about stuff that isn’t really in your wheelhouse.

  6. Quinn on June 10, 2015 at 1:28 am

    “A Variable card may order any number of Variables to receive the same number upon theirs at the same instant of time”

    That’s fantastic! You can store to multiple registers at the same time!
    I assume that means you will be able to specify multiple destination addresses on the variable card along with the number to be stored.

    I was wondering if there was a way to use numbers from a variable card more than once… Now I know it’s possible! That destructive read was worrying xD

    • Scott on June 10, 2015 at 8:59 pm

      “That destructive read was worrying xD”
      The Difference engine has a “sector wheel” that transfers the number from the source wheel to the destination wheel, then the sector wheel disengages from the dest. wheel and as it resets to zero it reloads the original value back into the source wheel. I’m sure the Analytical engine would have a similar capability.

      • Sydney Padua on June 10, 2015 at 11:43 pm

        Scott has it– each digit in the Store is registered on two wheels, so it can be read either destructively or non-destructively- the Variable card has the option!

  7. Scott on June 4, 2015 at 9:37 pm

    I didn’t have time to watch your videos before, but now I have. Very nice! You do a great job of explaining the workings. Babbage was quite clever to figure these things out, although I think he would have made his life much easier if he had chosen binary instead of decimal. Speaking of decimal, there doesn’t seem to be any provision for keeping track of decimal places. Was that left up to the human operators to worry about? Did the division function output remainders as a separate result?

  8. Scott on June 1, 2015 at 9:19 pm

    Hi Sydney!
    I don’t do Tweeting or FaBooking, but I wanted to say how much I enjoyed seeing you at the Computer History Museum. Also, how much fun it was to read The Book!
    You told us how painful it was to write it, so I want you to know your pain was my gain. I guess that makes me some sort of psychic-literary vampire. :-)

  9. Jim S. on May 31, 2015 at 5:14 pm

    Sydney, amazing work! Thank you for advancing the world’s knowledge of this subject!

    BTW, I’m surprised I don’t detect a British accent in your voice which, unlike your writing style, is distinctly British. :)

    • Scott on June 1, 2015 at 9:20 pm

      Jim S.
      She’s from Canada, that’s why.

  10. John on May 31, 2015 at 4:37 pm

    I love the “who would be stupid enough to try to use two variables at a time” response.

    I am, however, disappointed I wasn’t able to get out when you were in New York. I hope the tour went well.