News for hackers. Stuff that matters.

A comment on How could the early Unix OS comprise so few lines of code?. Parent comment

Re:How could the early Unix OS comprise so few lines of code? by inkyoto on Monday September 11, 2023 @06:08AM (#37465085)
> 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.

[ Parent | on HN ]
Re:How could the early Unix OS comprise so few lines of code? by thequux on Monday September 11, 2023 @12:04PM (#37469298)
The 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.
[ Parent | on HN ]
Re:How could the early Unix OS comprise so few lines of code? by inkyoto on Monday September 11, 2023 @11:44PM (#37476775)
You 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.
[ Parent | on HN ]