Warner Losh's Old-School Disk Partitions (via) is a discussion of how disk partitioning worked and evolved in the early days of Unix, up through 4.3 BSD. This has more information than what I wrote about how major and minor device numbers worked in V7, because I missed that various disk device drivers had their own partitioning tables for minor numbers.

Warner Losh's blog has a lot of interesting writing on historical Unix things, so if that's one of your interests (as it is one of mine) it's well worth a look in general.