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A comment on The SeL4 Microkernel: An Introduction [pdf]. Parent comment

Re:The SeL4 Microkernel: An Introduction [pdf] by ryao on Sunday March 23, 2025 @05:05PM (#43455906) 

  NT and XNU never had microkernel origins - Cutler explicitly refuted this at a conference in the early 1990s
Interestingly, the Tanenbaum–Torvalds debate had Tanenbaum claim otherwise at the very start:

  The alternative is a microkernel-based system, in which most of the OS runs as separate processes, mostly outside the kernel. They communicate by message passing. The kernel's job is to handle the message passing, interrupt handling, low-level process management, and possibly the I/O. Examples of this design are the RC4000, Amoeba, Chorus, Mach, and the not-yet-released Windows/NT.
https://groups.google.com/g/comp.os.minix/c/wlhw16QWltI

That is why I thought Windows NT had originally been intended to be a microkernel.

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Re:The SeL4 Microkernel: An Introduction [pdf] by p_ing on Monday March 24, 2025 @10:25PM (#43467568)
NT incorporates a client/server model, like a microkernel, but isn't a "pure" microkernel like Mach. This gives rise to the 'hybrid kernel' term, which Linus dislikes.

Wikipedia has a decent depiction of the hybrid structure, but quoting from the NT Design Workbook:

> This specification describes the kernel layer of the NT OS/2 operating system. The kernel is responsible for thread dispatching, multiprocessor synchronization, hardware exception handling, and the implementation of low-level machine dependent functions.

> The kernel is used by the executive layer of the system to synchronize its activities and to implement the higher levels of abstraction that are exported in user-level API's.

https://en.wikipedia.org/wiki/Windows_NT_3.1#Architecture

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