It's a qemu virtual machine with real hardware passed though. You know VT-x and VT-d. Apple's still makes the best desktop OS, but Linux as far surpassed the macOS and Windows as far as taking advantage of modern hardware. I haven't tried to boot Sierra from the NVME drive, as I want to use APSF and Sierra support is very limited, but I do boot from HS from it, and it works great. I have no need to go back to Sierra, everything works the same, but Apple seems to have dropped support of my old Firewire iSight. Tho that's OK because I haven't figured out the magic needed to pass a PCI FW card to qemu-system-x86_64 that OS X likes. I did pass one to qemu-system-ppc and it works fine under OS 9 and Tiger.