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VMS feels like DOS if DOS were actually secretly UNIX

Also, don't forget about OS/8 for the PDP-8 series. Very DOS-y, and released by DEC all the way back in '71.

VMS feels like DOS if that DOS was from another dimension. About the only thing they have in common is "DIR" and ".EXE" extensions.

Which is also why it's so fascinating Windows NT sort of merged both parallel dimensions with its influences directly from both DOS and VMS.