Minix was really the first of its kind; a Unix-like OS that you could run on cheap (relatively speaking at the time) commodity hardware and that you could get the source code for. A lot of the computing we take for granted now comes from Tanenbaum's work.
I first learned of Minix by reading about it in Byte magazine. At the time, I was an undergrad at a big US university, a member of the Association of American Universities. The only multitasking computers on the entire campus were a Unix mainframe, a VAX, and a cluster (lab) of Sun workstations that only graduate engineering students could have accounts on. The Unix and VAX machines could be accessed using VT-100 (and later) terminals in computer labs spread out all over the campus. There were also BYOF (Bring Your Own Floppies) computer labs filled with DOS (pre-windows) PCs, and a few labs filled with early Macs, but those labs were mostly used by humanities majors hunting-and-pecking their term papers out.
Booting a multitasking unix-like OS on a personal computer was a huge deal back then.