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Sadly, that is not entirely correct. Whilst all three BSDs (386BSD, FreeBSD, and NetBSD; there was no OpenBSD in the beginning) did inherit the legacy Mach 2.5-style design, it did not live on in FreeBSD, whose core team started pretty quickly replacing all remaining vestiges of the Mach VM[0] with a complete, modern, and highly performant rewrite of the entire VM. FreeBSD 4 had none of the original Mach code left in the kernel codebase, and that happened in the late 1990s. Therefore, FreeBSD can't be referenced in a relationship to Mach apart from the initial separation/very early foundation stage. NetBSD (and OpenBSD) went on for a while but also quickly hit the wall with the Mach design (performance, SMP/scalability, networking) and also set out on a complete rewrite with UVM (unified virtual memory) designed and led by Chuck Cranor, who wrote his dissertation on the UVM. OpenBSD later borrowed and adopted the UVM implementation, which remains in use today. So out of all living BSD's[1], only XNU/Darwin continues to use Mach, and not Mach 2.5 but Mach 3. There have been Mach 2.5, 3 and 4 (GNU/Hurd uses Mach 4) in existence, and the compatibility between them is rather low, and remains mostly at the overall architectural level. They are better to be treated as distinct design with shared influence. [0] Of which there were not that many to start off with. [1] I am not sure whether DragonBSD is dead or alive today at all. |
Oof, yeah.[0][1]. I hope they're doing alright - technically fascinating, and charming as they march to the beat of their own accordion.[2][3][4][5]
[0] https://www.dragonflybsd.org/release64/
[1] https://gitweb.dragonflybsd.org/dragonfly.git
[2] https://www.dragonflybsd.org/mailarchive/kernel/2012-03/msg0...
[3] http://www.bsdnewsletter.com/2007/02/Features176.html
[4] https://en.wikipedia.org/wiki/Vkernel
[5] https://en.wikipedia.org/wiki/HAMMER_(file_system)