Author here. Thanks for posting this. This is something I wanted to continue. The plan is still discussing NetBSD source code, as much as I can. Reading NetBSD code is a great way to learn operating systems! :-)
I always found it noteworthy in that the designers of Microsoft Windows did not consider co-existance with other OS on the same computer, i.e., "dual-booting". When I install NetBSD I never have to worry about it clobbering any code needed by other OS to boot. Not sure about today, but years ago Windows used to require being installed in the first bootable partition. If some other OS code occupied that position it was clobbered. On the other hand, the designers of NetBSD seem to have considered the possible co-existence with other OS on the same computer. To me, that is great design. NetBSD has this author's favorite bootloaders and I consider their kernels more flexible to boot than Linux kernels. I do not use grub. NetBSD has long supported the 1995 multiboot specification. Years ago, Linux did not. Perhaps that has changed. It always seemed like there were only a limited number of bootloaders that could boot Linux.
Oh, this is very nice:) One question: Why does this page open with a link to FreeBSD docs? (Just general information on x86 boot process? Is this code similar/shared between the BSD family members?)