Not sure about that. Segmentation as it was used on Intel CPUs before the 386 ("Real Mode", "Protected Mode") wasn't used in Linux (other then during the boot

Not sure about that. Segmentation as it was used on Intel CPUs before the 386 ("Real Mode", "Protected Mode") wasn't used in Linux (other then during the boot as PC BIOS was running in 8086 compatible Real Mode). Linus was quite outspoken about the awkward programming model of those earlier CPUs and there's a reason Linux started not before he got a 386 (he was accustomed to 32bit wide flat address space from the 68008 in his earlier Sinclair QL). Paging is an old OS concept and predates Intel CPUs and even Unix. How far back in time do you want to go? I think some concepts which were influential in the early days of Linux are well covered in Minix (1.0) code and book (after all, Linus first experimented with a 386 scheduler for Minix).