[TUHS] quick question on PDP-11 addressing

[Paul Winalski via TUHS]

On Mon, May 4, 2026 at 12:07 PM ron minnich via TUHS <tuhs at tuhs.org> wrote:

> related question, when people started getting their VAXes, what was the
> smallest configuration that ran Unix?
>

Originally the smallest memory configuration for the VAX-11/780 was 128KB.
My alma mater was a hardware beta test site for the VAX-11/780 (in 1977).
Our machine had 1MB of memory.  I joined DEC as a software engineer in
1980.  Nobody in the VAX software group knew of anyone running a 128KB VAX
of any model.  When VAX/VMS Version 4.0 came out in the mid-1980s there
were still a few (4 or 5) 512KB VAX systems out there running VAX/VMS.  VMS
V4 would not run properly with less than 1MB of memory.  After quite a bit
of bellyaching and wrangling DEC decided that it was cheaper to simply give
those 4 or 5 customers 512K more of memory for free rather than try to
shoehorn VMS V4 into 512KB.

For all later VAXen the minimum memory size was measured in megabytes.

I would imagine that Unix would have no problem running on a 128KB VAX
system, if any of those actually existed.  More likely the smallest Unix
configuration would be a 512KB VAX-11/725 or 11/730.

-Paul W.