I'm old enough to remember System 6 and later it's "Multifinder", which allowed the running of two programs at a time. Then the complete mess with multiple crashes with System 7. When System 8....sorry, "OS 8" came along, it fixed a lot of things, but it was still coopertative multitasking with no memory protections, which meant if something crashed, it could crash the entire system.
I remember watching my friends with Macs, back in the day, and they sure looked pretty, but the underlying architecture was archaic. I remember often saying (literally), “what this thing needs is demand-paged virtual memory and preemptive multitasking”. Then, Mac OS X came along, and it didn’t merely add those, it had switched over to my beloved Unix, complete with a FreeBSD userland! Gave it a couple years to mature (or get past being a toddler, at least), and dove in feet first. macOS is the best Unix workstation, and has been for a long time. What it loses in Unix purity (the case-mangling filter on the filesystem is still a black mark against it), it gains in having the nicest, most consistent GUI of any Unix, and support by commercial software that Linux could only dream of (yes, you can get Linux versions of some commercial apps, but not nearly the scope that macOS commands).
Linux stole BSD’s thunder by capturing the spotlight as
a x86 Unix(-alike) while BSD was mired in a frivolous lawsuit from AT&T (and, man, the Linux fanatics, many of whom had never seen a Unix before, showered Linux with praise and crowned it prom queen, and devoted huge efforts into improving it and proselytizing it, at a time when it wasn’t half the OS that FreeBSD was
*), but then macOS stole the desktop market for Unix that Linux was always promising itself (“next year will definitely be the year of Linux on the desktop”).
*: (To me, back in the day, it seemed like Linux was a beat up VW Bug that rolled into a town of Windows bicyclists who had never seen a car, and the Windows townsfolk all said, “Lo! This wondrous new device is a CAR! And it’s clearly the first and greatest CAR ever!” and then they set up a cult around it to spread the word to everyone that this was the greatest car ever and all should bow before it and bring it offerings... and when their missionaries reached people who were well acquainted with cars, those car people said, “you know, that’s fairly mediocre as cars go, we have these here that have been carefully designed and finely tuned over the decades—” “NO! You see, Linux is
FREE! That makes it the
best car ever!” “Uh, yeah, you see, all these BSD variants are free too, even more free than your Linux, and—” “NO, I say! Begone, heretic!
Shun the disbeliever!”. Anyway, that’s today’s Unix history lesson. Nowadays, I work on Linux servers, among others, but I do it from a Mac. Linux is a good solid OS these days, and great for servers - more by dint of huge efforts thrown at it over the years than because of its underlying design - but it’s still far from catching macOS as a desktop OS

)