I also appreciate your responses! I especially appreciate the correction about the Z80's power supply requirements.

> What's the energy efficiency difference between generating electricity with a hand crank vs. a nuclear reactor?

A hand crank is about 95% efficient. An electromechanical generator is about 90% efficient. Your muscles are about 25% efficient. Putting it together, the energy efficiency of generating electricity with a hand crank is about 21%. Nuclear reactors are about 40% efficient, though that goes down to about 4% if you include the energy cost of building the power plant, enriching the fuel, etc. The advantages of the nuclear reactor are that it's more convenient (requiring less human attention per joule) and that it can be fueled by uranium rather than potatoes.

> Even if you take into account all the inputs it takes to build and run the reactor, the overall output to input energy ratio is much higher. (...) The type of efficiency I'm thinking of is precisely the energy required to maintain and run something vs. the work you get out of it.

The term for that ratio, which I guess is a sort of efficiency, is "ERoEI" or "EROI". https://en.wikipedia.org/wiki/Energy_return_on_investment#Nu... says nuclear power plants have ERoEI of 20–81 (that is, 20 to 81 joules of output for every joule of input, an "efficiency" of 2000% to 8100%). A hand crank is fueled by people eating biomass and doing work at energy efficiencies within about a factor of 2 of the best power plants. Biomass ERoEI varies but is generally estimated to be in the range of 3–30. So ERoEI might improve by a factor of 30 or so at best (≈81 ÷ 3) in going from hand crank to nuclear, and possibly get slightly worse. It definitely doesn't change by factors of a thousand or more.

Even if it were, I don't think hand-crank-generated electricity is used by "plenty of people".

> projects like CollapseOS are specifically meant to create code that can handle low-level complexity and make these things easier to use and maintain.

I don't think CollapseOS really helps you with debugging the EMI on your RAM bus or reducing your power-supply ripple, and I don't think "ease of use" is one of its major goals. Anti-goals, maybe. Hopefully Virgil will correct me on that if he disagrees.

> if you were having to replace crystals, they are simple and low frequency, 2-16Mhz, and lots have been produced, and once again the fact that it uses parts that have been produced for decades and widely distributed may be an advantage.

I don't think a widely-distributed crystal makes assembly or maintenance easier than using an
on-chip RC oscillator instead of a crystal. It does have real advantages for timing precision, but you can use an external crystal with most modern microcontrollers just as easily as with a Z80, the only drawback being that the cheaper ones are rather short on pins. Sacrificing two pins of a 6-pin ATTiny13 to your clock really reduces its usefulness by a lot.

> If I look at archive.org for ATSAMD20 I come up empty, but Z80 gives me tons of results like...

Oh, that's because you're looking for the part number rather than the CPU architecture. If you don't know that the ATSAMD20 is a Cortex-M0(+) running the ARM Thumb1 instruction set, you are going to have a difficult time programming it, because you won't know how to set up your C compiler.

There is in fact enormously more information available for how to program in 32-bit ARM assembly than in Z80 assembly, because it's the architecture used by the Acorn, the Newton, the Raspberry Pi, almost every Android phone ever made, and old iPhones. See my forthcoming sibling comment for information about ARM programming.

Aside from being a much better compilation target for high-level languages like C, ARM assembly is much, much easier than Z80 assembly. And embedded ARMs support a debugging interface called OCD which dramatically simplifies the task of debugging broken firmware.

> models like [Z80s and 6502s] that have been manufactured for decades and exist all over might end up being a better fit

There are definitely situations where Z80s or 6502s, or entire computers already containing them, are more easily available than current ARM microcontrollers. (For example, if you're at my cousin's house—he's a collector of obsolete computers.) However, it's difficult to overstate how much more ubiquitous ARM microcontrollers are. The heyday of the Z80 and 6502 ended in about 01985, at which point a computer using one still cost about US$2000 and only a few million such computers were sold per year. The most popular 6502 machine was the Commodore 64, whose total lifetime production was 12 million units. The most popular 8080-family machine (supporting a few Z80 instructions) was probably the Gameboy, with 119 million units. We can probably round up the total of deployed 8080 and 6502 family machines to 1 billion, most of which are now in landfills.

By contrast, we find ARMs in things like not just the Gameboy Advance but the Anker PowerPort Atom PD 2 USB-C charger http://web.archive.org/web/20250101181745/https://forresthel... and disposable vapes https://ripitapart.com/2024/04/20/dispo-adventures-episode-1... https://old.reddit.com/r/embedded/comments/1e6iz4a/chinese_c... — and, as of 02021, ARM tells us 200 billion ARMs had been shipped https://newsroom.arm.com/blog/200bn-arm-chips and were then being produced at 900 ARMs per second.

That means about as many ARMs were being produced every two weeks as 8080 and 6502 machines in history, a speed of production which has probably only accelerated since then. Most of those are embedded microcontrollers, and I think that most of those microcontrollers are reflashable.

Other microcontroller architectures like the AVR are also both more pleasant to program and more abundant than Z80s and 6502s. They also feature simpler and more consistent sets of peripherals than typical Z80 and 6502 machines, in part because the CPU itself is so fast that a lot of the work these obsolete chips need special-purpose hardware for can instead be done in software.

So, I think that, if you want something useful and resilient in situations where people have limited access to resources, people who may still want to deploy some forms of automation using what's available, you should focus on ARM microcontrollers. Z80s and 6502s are rarely available, much less useful, fragile rather than resilient, inflexible, and unnecessarily difficult to use.