[freeone3000]

Windows has had subsystems since the OS/2 era, and WSL1 was actually such a subsystem. Initrix was the Microsoft POSIX Subsystem.

[EvanAnderson]

There was a POSIX subsystem in Windows NT before Microsoft acquired Interix (which became Windows Services for Unix).

[tobinfricke]

Yes, but the name "Linux Subsystem for Windows" would have been much less confusing.

[shawnz]

WSL1 isn't actually an NT subsystem like Interix was.