[TUHS] Is there a good, even definitive, list of reimplementations of the Unix kernel? What would good cut-off criteria be?

[Paul Winalski via TUHS]

On Sun, Apr 19, 2026 at 1:56 AM Peter Yardley via TUHS <tuhs at tuhs.org>
wrote:

>
> OSX uses a microkernel, Mach. Thing is more and more code got moved from
> user space into the kernel to speed it up. First OSF1 moved more code into
> kernel space, then NeXT, then Apple. But the kernel definitely started out
> as the Mach micro kernel.
>
> macOS (aka OS X) indeed uses the Mach microkernel, though a you say over
time code has been moved from user space to the kernel for performance
reasons.

macOS still uses Mach-O, the Mach object file and executable format.  When
Mach-O was first designed it was a big step up in flexibility and
functionality from a.out and COFF.  But compared to ELF, Mach-O is
functionally deficient and hard to use (from the perspective of compilers,
assemblers, and linkers).  I'm afraid that in terms of object and
executable formats, the world has moved on and left macOS (and Windows,
which uses a form of COFF) behind.

Linux uses ELF.  What are recent versions of Unix using?

-Paul W.

-Paul W.