Continuation:
The other approach is to learn and understand a modern single-board computer (SBC) such as a Raspberry Pi or the BeagleBone Black. However, the Raspberry Pis are not completely open source hardware, which means that some components are proprietary black boxes. The XINU educational OS runs on the BeagleBone Black [1], so that's probably a path to explore, but the community support and resources available for BeagleBone is likely to be less than that of Raspberry Pi, Commodore 64, and MS-DOS.