4 ms·
> the PDP-11 disk unit throwing itself around violently when somebody started nroff. That was the overlays… the early days substitute for the virtual memory pr
by inkyoto 3y ago
> the PDP-11 disk unit throwing itself around violently when somebody started nroff.
That was the overlays… the early days substitute for the virtual memory proper. If I remember correctly, the first PDP-11 to have the true virtual memory and a MMU was PDP-11/70 which had 18-bit wide hardware addresses.
- thequux 3y agoThe 11/70 had a 22-bit wide memory bus and an 18-bit wide unibus which was mapped to the high 256kb of the 4M physical address space.
- inkyoto 3y agoYou are correct. I have long forgotten about the mapped memory and was thinking about Unibus device registers having long 18-bit addresses. The 11/70 also had separate instruction and data spaces which did not exist in earlier models.