Its funny because I'm younger than you by a couple of years and I can remember the big parallel ports on keyboards before PS/2 became popular! PS/2 still feels modern to me in comparison
PS/2 and AT refer to the IBM computer models where the connectors were introduced, of course.
Our computer lab in college had these NEC/AT&T 386 desktops that had RJ-11 keyboard ports that didn’t work anywhere else.
I'm 33 and also grew up with computers that only had PS/2 ports! Granted, USB existed, but the PCs I had as a youngster were old PCs.
I'm quite sure I literally used the adapter mentioned in the submission, as one of the first mouses I bought myself was a Microsoft mouse that came with a PS/2<>USB adapter!