Original link: Hacking wizard gets Linux to run on a 1971 processor, though it takes almost 5 days to boot the kernel / PCGamer.
Actually he booted Debian for MIPS on a R3000 emulator running on the Intel 4004. But 5 days to boot is a long time. The slowest boot I remember was a MicroVAX booting on 9 track tape (to perform a backup of the system disk) which took a half hour or so. But then 790 KHz 4 bit CPU with 4 KB of RAM is pretty small.