Sure, I linked it in. I posted the first response from my phone, took me a bit to find everything on my computer...
The PDP-11 has an MMU and supports what's essentially segmented memory (https://gunkies.org/wiki/PDP-11_Memory_Management), with different address spaces for a kernel and for a userspace. It also supports a 22-bit "real" address space, hence when 2BSD and other "older" PDP-11 unixes can use up to 4MB of real memory (and 2.10BSD's kernel actually used more memory than could fit in a 16 bit address space at once -- needing to be manually chunked and loaded in/out of memory. In the release notes (http://www.krsaborio.net/bsd/research/1987/0715.htm) the authors said "Yes, [this is the last release] at least by us; quite frankly, we'd rather sacrifice our chance at heaven than look at a 16-bit machine again.", so it's about as nightmarish as it sounds.
It doesn't support paging, though, so no real virtual memory. I'm not really sure how thorough the process isolation was -- I know in the early releases, there was basically none, and a bad user process would crash the whole machine. I believe by later models (the MMU did change over time) it was "good enough" to keep the userland from crashing the kernel, at least.
Wasn't until 3BSD from Berkeley that proper virtual memory was added -- hence why the kernel's name was changed from /unix to /vmunix. Which is where the "vm" in "vmlinux" comes from, in case anyone's curious.
> Wasn't until 3BSD from Berkeley that proper virtual memory was added -- hence why the kernel's name was changed from /unix to /vmunix. Which is where the "vm" in "vmlinux" comes from, in case anyone's curious.
The PDP-11 has an MMU and supports what's essentially segmented memory (https://gunkies.org/wiki/PDP-11_Memory_Management), with different address spaces for a kernel and for a userspace. It also supports a 22-bit "real" address space, hence when 2BSD and other "older" PDP-11 unixes can use up to 4MB of real memory (and 2.10BSD's kernel actually used more memory than could fit in a 16 bit address space at once -- needing to be manually chunked and loaded in/out of memory. In the release notes (http://www.krsaborio.net/bsd/research/1987/0715.htm) the authors said "Yes, [this is the last release] at least by us; quite frankly, we'd rather sacrifice our chance at heaven than look at a 16-bit machine again.", so it's about as nightmarish as it sounds.
It doesn't support paging, though, so no real virtual memory. I'm not really sure how thorough the process isolation was -- I know in the early releases, there was basically none, and a bad user process would crash the whole machine. I believe by later models (the MMU did change over time) it was "good enough" to keep the userland from crashing the kernel, at least.
Wasn't until 3BSD from Berkeley that proper virtual memory was added -- hence why the kernel's name was changed from /unix to /vmunix. Which is where the "vm" in "vmlinux" comes from, in case anyone's curious.