On his blog, Dmitry Grinberg writes
about getting Linux to run on an 8-bit microcontroller. In order to do so, he wrote an ARM emulator for the ATmega1284p. The results: "uARM is certainly no speed demon. It takes about 2 hours to boot to bash prompt ("init=/bin/bash" kernel command line). Then 4 more hours to boot up the entire Ubuntu ("exec init" and then login). Starting X takes a lot longer. The effective emulated CPU speed is about 6.5KHz, which is on par with what you'd expect emulating a 32-bit CPU & MMU on a measly 8-bit micro. Curiously enough, once booted, the system is somewhat usable. You can type a command and get a reply within a minute. That is to say that you can, in fact, use it. I used it to day to format an SD card, for example. This is definitely not the fastest, but I think it may be the cheapest, slowest, simplest to hand assemble, lowest part count, and lowest-end Linux PC. The board is hand-soldered using wires, there is not even a requirement for a printed circuit board.
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