| > But Linux doesn't have the concept of a "subsystem", that's pretty much a Windows NT exclusive (inherited from its core predecessor OS/2) Mainstream OS/2 doesn't have "subsystems" in the sense that Windows NT does, so it is mistaken to suggest that Windows NT got the idea from OS/2. Something like the NT "subsystem" concept is in the abortive IBM Workplace OS which became OS/2 PPC edition. Workplace OS is based on the Mach microkernel and designed to run both Unix and OS/2 as "personalities". But this was never released for x86, and the PPC port was only ever released in beta form and abandoned before GA. I think Windows NT more likely got the idea from Mach than mainline OS/2. Mach calls them "personalities" not "subsystems" (although some people will use the word "personality" when talking about NT). If you look at the internals of macOS/iOS/Darwin/XNU, the Mach personality concept survives in highly vestigial form – XNU has its core Mach APIs (Mach personality) and BSD APIs (BSD personality). In principle Apple could add some third personality (e.g. Windows personality, Linux personality, Android personality, etc) but they probably never will. (CMU Mach was always intended to support multiple OS APIs, but the CMU Mach developers only ever implemented a BSD Unix personality, and Workplace OS's OS/2 personality was one of the few cases of anyone ever implementing a non-Unix personality on top of Mach; the BSD personality of XNU is a descendant of CMU Mach's original BSD personality, but updated with a lot of newer code from FreeBSD and also of NeXT/Apple's own devising) NT drew a lot of influence from VMS, and VMS also has "subsystems", although VMS' subsystems have little in common with NT's other than the name. Other operating systems also have subsystems – for example, the Job Entry Subsystem (JES) is a major component of IBM's mainframe operating system z/OS (formerly known as MVS), but z/OS subsystems and NT subsystems have little in common other than the name as well. "Subsystem" is popular as a generic term for an OS component. Also, as other respondents have pointed out, WSL1/WSL2 are not subsystems in the classic Windows NT sense. |