I've been reading through [The Unix Hater's Handbook](https://simson.net/ref/ugh.pdf). It has many, *many* very valid criticisms. (I'm still raging that terminal escape codes aren't in the terminal driver...)

There is one anomaly though: One of the chapters is complaining that Unix doesn't support "file versioning", when "real operating systems" have had this feature for years.

Now they don't really elaborate on what that means, but it *seems* to mean a system where each time you save a file, the old version is still kept, and the new revision just gets a new version number.

I am not personally aware of *any* operating system in the entire history of computing *ever* having had this feature. Can someone enlighten me as to what these mythical systems were?

Unix was written an extremely long time ago. As I understand it, in Those Days a "large" system might have as much as 2 kilowords of memory and presumably a similarly tiny amount of disk. The "real operating systems" the book alludes to would presumably be even older than Unix, and hence for even more constrained hardware.

I find it *very* hard to believe that a system with a 4 Kword disk would "waste" disk space by keeping every prior version of every file ever created. That just seems like you'd run out of disk space within ten minutes.

Have I misunderstood what they're talking about? Or were there actually systems that worked like that?