Comment by lproven

I know.

Most of why DOS, Windows, OS/2, WinNT and all of Windows 11 and Windows Server today are how they are -- the name-dot-three-letter-extension filenames, the directory structure, drive letters, the basic commands, the config file formats, all of it -- owes to ancestry in DEC OSes.

Gary Kildall worked with DEC minis. He wrote CP/M in PL/M, designing it to be a DEC-like OS for the new Intel 8080.

DR did great. Became big. It was very slow with CP/M-86 for the new 8086. So, Tim Paterson of SCP wrote his own tiny OS in assembler that used the documented public CP/M API, but the disk format from Microsoft Standalone Disk BASIC. (That's now called "FAT".)

MS licensed it, and later bought it, and renamed it MS-DOS.

MS-DOS is a reproduction of a reproduction of a DEC OS.

Mostly TOPS-10.

https://www.os2museum.com/wp/why-does-windows-really-use-bac...

TOPS-10 ran on the PDP-10, the big brother of the PDP-6, which is the direct ancestor of the PDP-7 on which UNIX was built.

Some effort went into OS/2 and some of that influenced NT. NT was build with an input of code from the big brother of the PDP-11 OS. No wonder it's DEC-like: it's got direct DEC ancestry on one side and indirect on the other. It's the offspring of 2 cousins.