I disagree. I remember running Minix on a no-name 8088 machine with 640K of RAM and no hard drive at all. Unix was developed on machines with far less resources than that. It is not a particularly heavy-weight OS.
Sure, Minix would run on a low-end system, but to have taken the place of Microsoft Windows as the successor to DOS you would have needed a GUI like X which Minix did not have.