Russinovich claims it was an OpenVMS clone and upgrade with some convincing evidence: https://www.itprotoday.com/compute-engines/windows-nt-and-vms-rest-story

Russinovich claims it was an OpenVMS clone and upgrade with some convincing evidence: https://www.itprotoday.com/compute-engines/windows-nt-and-vms-rest-story https://www.itprotoday.com/compute-engines/windows-nt-and-vm... That gave them a huge lead in developing a server-grade OS. They probably just used OS/2 for the OS/2 part that ran on top of it. Fast forward to today, the result still isn't robust as its predecessor in cluster configuration or the AS/400 Microsoft ran on before using their own product. They did show how much better VMS could've been as a desktop... by dominating on the desktop. :)