Relating this back to the topic of OS history, it's interesting to note that PDP-11 was the original BSD UNIX platform, and that 2.11BSD for PDP-11 still receiv

Relating this back to the topic of OS history, it's interesting to note that PDP-11 was the original BSD UNIX platform, and that 2.11BSD for PDP-11 still receives occasional patches (the most recent one I can find is from March of last year). And as a former "home" MicroPDP-11/83 owner, I can attest that it was indeed fun to put together and write code for. With that said, while probably not what you have in mind when you speak of "single-board systems", the DEC Professional 3xx (325, 350, 380) is a desktop PC built around a single-board PDP-11 CPU. And most (all?) MicroPDP-11 systems are built around a Q-Bus CPU board, and, excluding bulky options like multi-port serial patch panels, open-reel tape drives, and large (around 150 lbs. and 6U for my 456MB RA81) hard drives, aren't much bigger than a modern full-tower or >1U rack server, though they require considerably more electrical power (generally not too much for a dedicated 120V 15-20A household circuit, however, unless kitted out with, e.g., more than one of the aforementioned RA81 disks). Both are "single-board systems" in the sense that the CPU, and in some cases RAM, is contained on a single board, though you'll need one or more I/O boards to do anything useful with them. Which, depending on your idea of fun, you could, I suppose, build yourself — there was, after all, a time when PDP-11 CPUs weren't an unusual choice in larger embedded systems.