Correct me if i am wrong but isn't the NT design heavily based off of (some would say a rip off of) VMS, Microsoft having poached much of DEC's OS dev team including chief architect David Cuttler.
Yes, and DOS inherited things from older DEC operating systems like TOPS10 (which IIRC was the first occurrence of using /forwardslash options on the command line).
Many are under the mistaken impression that DOS got forward slash as an option character from CP/M or from IBM. CP/M denoted options using square brackets, and IBM mainframe operating systems generally indicate options using parenthesises. (The usage of square brackets appears to be a modification of IBM's approach; I'm not sure why Gary Kildall made that change – before creating CP/M, he'd used IBM CP/CMS at the Naval Postgraduate School, which likely influenced both this option style, and also drive letters.)
My own reconstruction of what I think happened (this was all before I was born, I'm just making some inferences based on what I know about the topic) – Microsoft was heavily influenced by DEC operating systems (Bill Gates and Paul Allen wrote the first version of Microsoft Basic on a PDP-10). Microsoft didn't like CP/M's native option syntax, so for their development tools for CP/M, they adopted a DEC-style option syntax instead. Since many ISVs used Microsoft's development tools, a lot of third party software on CP/M ended up using the same option syntax too. Tim Paterson at Seattle Computer Products was influenced a lot by Microsoft (even before he worked for them), so QDOS/86-DOS/PC-DOS/MS-DOS ended up with the DEC/Microsoft-style forward slash as an option character. When DOS 2.0 came around, Microsoft wanted to switch it to dash/minus, for better Unix/Xenix compatibility. In support of this, they added a CONFIG.SYS setting SWITCHCHAR= to let you choose between forward slash and dash/minus, and an API (INT 21,37) to get/set that config setting at runtime. However, it was decided that the backward compatibility cost of that change was too great, so they pulled the feature from the documentation (although it still existed in the code; in later DOS versions, they disabled the ability to change it to anything other than forward slash, but the undocumented API to get the setting was never removed.)
