Xenix was my first UNIX experience, in 1993 at trade school during OS design classes.

The teacher would bring a single tower (486 based I think), plug it into monitor and keyboard, and the whole class would take 15 minute slots at it.

We would prepare our exercises in MS-DOS, with Turbo C 2.0, using mocks for the UNIX APIs.

Then use those 15 minutes to replace the mocks with the real deal, and have a go at it.

Failing the exercise, it was back to MS-DOS / Turbo C, while trying to figure out with pen and paper what might have gone wrong.

Then people complain nowadays when their build takes longer than 1 second.