blog: home computing: review unconventional computing

content/blog/2022-05-26-home-built-computation/index.md

@@ -45,7 +45,49 @@ context is that they're very labor intensive to manufacture/assemble.
 
 ## Non-Silicon Forms of Computation
 
-TODO: mention: https://en.wikipedia.org/wiki/Fluidics
+Wikipedia has an entire page on [Unconventional Computing](https://en.wikipedia.org/wiki/Unconventional_computing),
+and it's not even complete. there's also
+[Fluidics](https://en.wikipedia.org/wiki/Fluidics),
+[Optical Computing](https://en.wikipedia.org/wiki/Optical_computing),
+[Chemical Computing](https://en.wikipedia.org/wiki/Chemical_computer)
+[Electrochemical Transistors](https://en.wikipedia.org/wiki/Organic_electrochemical_transistor),
+and of course, vacuum tubes!
+
+these things aren't just the realm of theory. they all had use before the reign of the transistor:
+- vacuum tubes were the go-to before transistors. TODO: link.
+- the [MONIAC](https://en.wikipedia.org/wiki/MONIAC) used fluids to model economic activity.
+- OECTs are used in bio-sensing applications because they're safer than silicon in such settings. TODO: link
+
+the point of listing these is break the misconception that computation _must_ take place on silicon,
+or even semiconductors in general. the most alluring technology for my purpose looks to be _ferromagnetics_.
+
+magnetic core memory was widespread before we had integrated circuits. the [Apollo Guidance Computer](TODO) used core memory for its program data.
+lesser known, the [Elliott 803](https://en.wikipedia.org/wiki/Elliott_803#Hardware_description) repurposed core memory _into logic gates_.
+
+magnetic cores are _really simple_: you have some ferromagnetic material which has some interesting, often _nonlinear_
+relationship between its electric and magnetic field, and you have some conductor (copper) to carry these fields from
+one place to another. that's two, easily procurable materials, plus an insulator (air). and it's all solid state
+and (at a high level) operates on classical mechanics -- making it _scale independent_: a 1cm
+core behaves roughly the same as a 100um core, only with power scaled accordingly. you don't _need_ precise fabrication, so
+with some effort it should be possible to manufacture an integrated circuit out of these materials using something
+like selective laser sintering (which could pair nicely with non-electronic home-manufacturing).
+
+## Ferromagnetic Computing
+
+it's widely known that _any_ combinatorial circuit can be reduced to a representation which uses _only_ NAND gates
+(this includes flipflops, allowing not just combinatorial logic but also volatile storage, and hence general-purpose computation).
+one could alternatively use NOR gates, XOR gates, or inhibit gates (`Y = A and not B`).
+
+the Elliott 803 demonstrates a sort of inhibit gate, at an analog level: `Y = A - B` (based on the gate wiring, it could perform `Y = +/-A +/- B +/- C` with the sign configurable).
+the reason it required transistors is because these analog operations were _lossy_, and needed amplification to achieve the desired digital operation.
+that is, the "inhibit gate" might actually look something like `Y = 0.5*A - 0.5*B` and in order to feed this into the next gate you would need to amplify `Y` by 2,
+which a transistor does nicely.
+
+but that's not to say one _couldn't_ perform this amplification using ferromagnetics. in fact, magnetic amplifiers are all around us: _transformers_.
+
+can we assemble these components into one of the primitive digital logic gates?
+
+## TODO: review magnetic core theory
 
 
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