[johncolanduoni]

I mentioned XNU below. It doesn’t really count as a microkernel if you, you know, don’t actually use the microkernel part. At least for the 30 years between the FreeBSD collision and the introduction of DriverKit, which does most of its IPC through shared memory (because the mach ports are not efficient enough, I would assume).

[saagarjha]

Yes, but a lot of other things use Mach messages.

[johncolanduoni]

All the major OSes have components of the larger operating system that run in userspace and communicate via IPC, including Linux. But userspace drivers and basic system services (VFS, network stack, etc.) are very limited in their use of userspace/IPC. If macOS is a microkernel in the sense of those built on L4, then so are Windows and Linux, and the word doesn't have any meaning anymore.

[saagarjha]

Is that IPC called Mach?

[johncolanduoni]

Yes, and it’s quite inefficient compared to L4 or Zircon’s IPC so it isn’t used for anything that wouldn’t work just fine over a SEQPACKET socket using SCM_RIGHTS like Linux does. Is modern Windows a microkernel because ALPC exists?