Programmer 8-bit Show And Tell managed to mod his 1 MHz Commodore 64 to mine Bitcoin. This is a remarkable feat for hardware that's close to 40 years old. However, at 0.3 H/s, the system will take nearly a billion years, just to turn a profit of US$10.
https://www.notebookcheck.net/Commodore-64-from-1982-manages-to-Bitcoin-but-only-at-0-3-H-s.535232.0.html