If you crave experiencing or reliving what computing was like “back then” you have a lot of options. One option, of course, is to load an emulator and pretend like you have the hardware and software you are interested in. Another often expensive option is to actually buy the hardware on the used market. However, [mit-pdos] has a different approach: port the 6th edition of Unix to RISC-V and use a modern CPU to run an old favorite operating system.
It isn’t an exact copy, of course, but Xv6 was developed back in 2006 as a teaching operating system at MIT. You can find resources including links to the original Unix source code, commentary on the source code, and information about the original PDP 11/40 host computer on the project’s main page.
In addition, you might find the book about Xv6 of interest. We know you probably don’t want to use 1970’s-era Unix as your daily operating system, but you can learn a lot by even reading either the original code or the more up-to-date Xv6 source. It also isn’t a bad way to understand RISC-V internals.
Several computer science operating system classes use Xv6 in one form or another. You can see one of several lectures about it from Harvey Mudd College, below. We’ve covered RISC-V for a while because we like its openness. Not to mention, the CPU doesn’t have to be complicated.