Modern Baby: A pioneering computer from Manchester
7 comments
·March 11, 2025rlpb
jecel
"No-one would claim that a modern Harvard Architecture computer with its program stored in ROM isn’t a stored-program computer. So does ENIAC take the prize from Baby as the first electronic stored-program computer?"
I do actually claim that a modern Harvard Architecture computers such as the AVR8 or PIC microcontrollers are not stored-program computers. You can't store a program in them and then execute it. To be fair, some MCUs can change their own Flash so the difference can be subtle - in that case the processor is used either normally or as part of the ISP (in-system programming) circuit at different times.
For very simple stored-program machines the ability to modify running code is needed for it to be Turing complete. In a computer like the Baby, how would you add two arrays? It had no index registers. So you would need to increment the instructions that load and store from the arrays every time you go through the loop. I agree that this isn't an issue on a machine with only 32 words of memory in all, but it is a key idea in theory.
Of course, a Harvard computer can simulate a Von Neumann one (see AVR8 simulating an ARM in order to boot Linux where it does indeed store programs and then run them). In fact, a popular way to implement CISC computers was to build a tiny Harvard machine running a single program in its "microcode ROM" emulating the computer you actually wanted to use.
apignotti
You can play with an online simulator of this machine here: https://davidsharp.com/baby/online/index.html
The simulator is originally written in Java, and the browser version is powered by CheerpJ, a WebAssembly-based JVM (https://cheerpj.com/)
nonrandomstring
I totally love this early principle [0] for RAM by literally writing in electrons on a 2D surface and then reading them back using the electron gun.
tliltocatl
Fascinating that Willams tube (and Atanasoff–Berry computer's electrostatic drum) is in some way much closer to modern DRAM and flash than ferrites that were so revolutionary back then (or acoustic delay lines for that matter).
AndrewOMartin
See also acoustic delay lines. Basically the same but instead of using phosphorous, they use mercury, or piano-wire, but never gin. Gin was proposed by some fanciful idiot [1] but never used.
[1] https://en.wikipedia.org/wiki/Delay-line_memory#cite_ref-3
stevefolta
> In the ENIAC the form of the [sic] that [program] storage (decimal) was quite different to that of the data that ENIAC operated on (binary).
Huh? ENIAC was a decimal machine all the way through.
> Was the modified ENIAC less of a computer than the Manchester Baby because its program was in ROM and could not be changed by the computer?
To me, the most remarkable property of a computer is that data and code are interchangeable. This makes it possible for the same computer to run different programs, run programs that transform programs, and so forth. It's the same fundamental concept that today means that one can "download" an app and then run it.
(See also: Lisp, which is equally remarkable in the software space for the same reason)
> Look at it this way: many modern microprocessors, especially small ones for embedded control, have their programs in ROM. If they are modern-style computers, then so was the modified ENIAC.
What makes them modern-style computers, though, is that they are capable of having their firmware flashed - or at least the development versions can do this while their software is engineered. If the final product only runs a ROM, it has lost the essence of a general purpose computer, which is the fundamental and very remarkable invention that is what we actually celebrate.