> I suppose in principle the RPi Pico could self-host its own OS and devel environment. 520 KB of RAM in the old days was plenty to fit an OS and compiler.

With two cheap PSRAM chips and a bit of trickery, you can upgrade that to 32(.5) MB, which is certainly enough to run a small OS.

In principle you can add even more memory with bank switching, but 32 MB is the limit for a flat address space.

Window 95 ran on 8mb of ram.

The first Amigas had 512k of ram. Both had much less processing power.

With 32mb you could probably run some kind of Linux.