I'm no Windows architecture guru, but I think it's misleading to say it used VMs. These certainly weren't VMs in the way we now understand them. I think they were simply protected memory segments, with DOS boxes replicating the state of a DOS emulation layer. Also, Windows 3.1 (and possibly before) already used Protected Mode (anyone remember General Protection Faults?). Maybe Win95 made this compulsory?Windows 95 ... System stability was significantly increased by running multiple virtual machines under the OS.