With your birth as our starting point, then, let's look at the biggest desktop OS milestones of the past 40 years.
Unix was brought to life on a spare DEC PDP-7 at AT&T Bell Labs. When AT&T decided to abandon the Multics (Multiplexed Information and Computing Service) operating system on its minicomputers, Ken Thompson and Dennis Ritchie cobbled together an operating system so they could continue to play a space travel game that Thompson had developed. A colleague gave the system a jokey name based on Multics -- UNICS, the Uniplexed Information and Computing Service, which morphed into UNIX or Unix.
Intergalactic Digital Research's maverick brain Gary Kildall creates CP/M, a simple microcomputer operating system for simple microcomputers. It would be the model for command-line DOS variations for two decades.
The godfather of open source is born when the Computer Systems Research Group at UC Berkeley releases a variant on Unix called the Berkeley Software Distribution. BSD will ultimately spawn alternatives to some commercial microcomputer operating systems -- and form the core of at least one major commercial operating system, Mac OS X.
Tandy/Radio Shack introduces a line of affordable home computers, and debuts a family-friendly operating system called TRS-DOS with such Rated-M-for-Mature commands as KILL. Other companies' versions of DOS substitute the less menacing DEL command, for Delete.