During an annual purge of old file boxes, I came across my 5 1/4 CoCo disks. Much of what I know about unix and linux actually dates back to OS-9 on the CoCo:
Even on the CoCo, a quite minimalist hardware platform, it was possible under OS-9/6809 Level One to have more than one interactive user running concurrently (for example, one on the console keyboard, another in the background, and perhaps a third interactively via a serial connection) as well as several other non-interactive processes. -- OS-9 - Wikipedia
I wrote a shell in assembler; I ran across a hardcopy of the source a week or so ago. I wonder if the source is on these floppies. I made a copy on CD a few years back before I de-commissioned my last 5 1/4 disk drive.