Comment by 🚀 stack
Re: "What is analog computing? The basic idea is there is some…"
Yes! Yes! [Wildly gesticulating with his sliderule]
2025-12-24 · 4 months ago
16 Later Comments ↓
look up ball-disk integrator, ballistic computer installed on WWII era battleships are all build around it.
Some beauty from the past
👻 darkghost · Dec 25 at 11:01:
This discussion may not continue without mentioning the Curta mechanical handheld calculator.
charles petzold, author of 'code' has an amazing conference talk about it.
🚀 Analog_Guy [OP] · Dec 26 at 18:06:
The Curta is interesting. But by my definition, it is not an analog computer. It is a mechanical digital computer, using algorithmic steps to complete operations. Data is stored in memory registers, and then assigned steps are followed to manipulate the registers or transfer data between the registers, like in a modern digital computer.
In analog computing, the device or circuit itself physically models or represents the calculation. E.g., in an electronic analog computer, a calculation involving two integrations and a multiplication would involve patching together two integrators and a multiplier. It could be turned into a differential equation by patching the output of the last integrator to the input of the first.
🐦 wasolili [...] · Dec 26 at 18:25:
A couple years ago I impulsively picked up a copy of "Analog and Hybrid Computer Programming" by Ulmann, read a little bit, lost interest and forgot about it.
Maybe it's time to finally read it.
🚀 Analog_Guy [OP] · Dec 26 at 19:28:
I'm a close friend of Professor Ulmann. Or rather, I send him questions occasionally over e-mail, and he sends me replies in the hopes that I'll stop bothering him.
I studied his other textbook, "Analog Computing", which was a great read. I had to borrow it through inter-library-loan because I am on a tight budget. I believe he is working on a third edition of that. I haven't been able to get a copy of "Analog and Hybrid Computer Programming" yet. Older books on analog computing, from the 60s and 70s, are easy to find at university libraries.
I have to look into it! Programming an analog computer must mean something different than what we refer to as programming...
🚀 Analog_Guy [OP] · Dec 26 at 22:11:
Yes, in conventional computing, we come up with an algorithm which we feed into the computer as a set of instructions for it to follow to complete the computation. In analog computing, we construct or patch together the computational system, along with maybe some initial conditions. When you set up the relative positioning of the scales on your slide rule, the computation is already complete, though the results have to be interpreted. Electronic analog computers need initial voltages to be set in the integrators, and then, after switching to OP mode, the voltages vary and system solves itself.
👻 darkghost · Dec 26 at 23:31:
Debugging is often a brush and contact cleaner.
Also, percussive debugging
🚀 Analog_Guy [OP] · Dec 29 at 15:41:
In practice, the three most commons problems I have are (1) forgetting one of the patch cables while building a circuit, (2) my oscilloscope lead is not attached securely, and (3) I have my oscilloscope connected to the wrong output, so I'm seeing bad data and don't understand why.
As someone who has done much software but also a lot of hardware including high-speed digital PCB design, I have to say that analog circuits scare me stiff. I've seen things.
🚀 Analog_Guy [OP] · Dec 29 at 19:56:
The discussion is clouded by ambiguity. "Analog" is usually taken to mean "continuous" vs. discrete. It also can mean "analogue" — similarity — a form of computing where the computational system is a physical analogue to the computation being performed.
An analog computer can be made of digital components. Digital Differential Analyzers (see Wikipedia) were used for a short time in the late 60s. The compute components were digital, and were clocked together. But they were distinct computational units that were patched together to make a circuit mirroring the computation. They could do some things traditional electronic analog computers could not do, but were more esoteric to operate.
I've never heard of 'analog computing' used as in modeling some behavior. Have you really?
🚀 Analog_Guy [OP] · Dec 29 at 21:32:
Professor Ulmann gives a similar explanation in his book, "Analog Computing", ISBN 978-3110787610. I do not have the book on hand, right now, or I would try to give a better reference. I believe he also pointed out that analog computing does not mean "non-discrete" as even electronic analog computers are computationally discrete down at the electron level.
The core idea is that there is a physical analogue between the computation and the computational device. "Modeling some behavior" is not exactly the same thing as that, although modeling behavior was a very common use of electronic analog computers. Slide rules are analog computing devices, but they do not really model or simulate any system.
Original Post
What is analog computing? The basic idea is there is some physical analog between the computing device and the computing to be performed. A slide rule is a non-electronic computing device in which the analog is physical distances on logarithmic scales. A traditional electronic analog computer represents values as varying voltages which are feed through computing elements like integrators and multipliers.