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

[Dan Cross via TUHS]

On Sun, Apr 19, 2026 at 11:04 AM John Cowan via TUHS <tuhs at tuhs.org> wrote:
> On Sun, Apr 19, 2026 at 10:20 AM Paul Winalski via TUHS <tuhs at tuhs.org> wrote:
> > Linux uses ELF.  What are recent versions of Unix using?
>
> Solaris/Illumos, the major BSDs, QNX, BeOS/Haiku, IBM TPF, Stratus
> VOS, RISC OS, and Fuchsia are all Posix (at least), are still
> maintained, and have adopted ELF.

OpenVMS on x86_64 (and maybe Itanium?) also uses ELF. They even
modeled the calling convention for x86_64 on the System V ABI:
https://docs.vmssoftware.com/vsi-openvms-calling-standard/#DIFFS_FROM_x86-64

It's a mad, mad, mad, mad world.

> PE is used by Windows and its clone
> React/OS, the Mono framework for the CL, and UEFI.  Mach-O is used by
> iOS as well as macOS.

The one big advantage of Mach-O as far Apple is concerned are
so-called "universal" binaries, that can contain object code for more
than architecture. They made heavy use of this when transitioning from
PowerPC to x86, and are doing so again now, as x86 Macs are phased out
in favor of (ARM-based) Apple Silicon.  I don't think there's a
standard for doing something similar with ELF, though there was
something called "FatELF" that made an attempt.  It appears to be
defunct now.

        - Dan C.