[TUHS] Can PDP-11/23 PLUS run Unix?

[Phil Budne via TUHS]

Noel Chiappa wrote:
> Also (unrelated to the above, but since I'm posting) use of overlays in the
> kernel, useful on machines without separate I+D, came in with BSD 2.9:
>
>   https://gunkies.org/wiki/2.9BSD
>
> but it's poorly docuented; what I could find is linked there.
>
> 	Noel

V7M has overlays (c. 1981), I have 1983 as the date for BSD 2.9.

https://www.tuhs.org/cgi-bin/utree.pl?file=V7M/sys/conf/mch_ov.s contains:

/ machine language assist
/ (OVERLAY KERNEL VERSION)
/ for non-separate I & D space CPU's
/ 11/23, 11/24, 11/34, 11/40, & 11/60 CPUs
/ Fred Canter 8/3/81
/
/ Many thanks to Bill Shannon for the overlay kernel modifications.

There's some discussion in
https://www.tuhs.org/cgi-bin/utree.pl?file=V7M/doc/setup

    The first step is to select the type of
    unix system most appropriate to your CPU, there
    are three; unix_id for the separate I & D space
    CPUs (PDP11/44, PDP11/45, PDP11/55, & PDP11/70);
    unix_i for the non-separate I & D space CPUs
    (PDP11/23, PDP11/24, PDP11/34, PDP11/40, & PDP11/60);
    unix_ov the overlay text kernel for the non-separate
    I & D space CPUs.
    The size limitations of the unix_i kernel
    makes its use as an actual unix system
    inappropriate, its only purpose in life is
    to initially load unix from the distribution tape.
    The overlay text unix kernel should be used
    as the multi-user unix system on the non-separate
    I & D space machines.

The overlay kernel is loaded (linked) by:
https://www.tuhs.org/cgi-bin/utree.pl?file=V7M/sys/conf/ovload