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

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

[ROBERT MYERS via TUHS]

I’ve just obtained a 11/23 Plus system off of EBay and plan to get a QBone to emulate memory along with a few other things.  I need to know if Floating Point support is a requirement as well if I can also emulate up to 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
Sent from my iPhone

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

[Madeline Autumn-Rose via TUHS]

iirc 11/23 lacks supervisor mode so you’d be limited to the 2.9 port with MSCP but it’s been a bit so I could be mistaken

Sent from my iPhone

> On Feb 26, 2026, at 14:52, ROBERT MYERS via TUHS <tuhs@tuhs.org> wrote:
> 
> I’ve just obtained a 11/23 Plus system off of EBay and plan to get a QBone to emulate memory along with a few other things.  I need to know if Floating Point support is a requirement as well if I can also emulate up to 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
> Sent from my iPhone

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

[Clem Cole via TUHS]

https://gunkies.org/wiki/PDP-11/23#:~:text=hampage.hu,are%20no%20problems%20with%20this.


To your questions. Because it lacks separate I/D
Space and does not support supervisor mode (only user and kernel) 2.11BSD
will not work.  However V6 and V7 are possible. I think Ultrix-11 should be
able to work and is more likely to have the low level details that 11/23
will need.


Sent from a handheld expect more typos than usual


On Thu, Feb 26, 2026 at 5:52 PM ROBERT MYERS via TUHS <tuhs@tuhs.org> wrote:

> I’ve just obtained a 11/23 Plus system off of EBay and plan to get a QBone
> to emulate memory along with a few other things.  I need to know if
> Floating Point support is a requirement as well if I can also emulate up to
> 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
> Sent from my iPhone
>

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

[Madeline Autumn-Rose via TUHS]

v7m is also an option
Sent from my iPhone

> On Feb 26, 2026, at 15:03, Clem Cole via TUHS <tuhs@tuhs.org> wrote:
> 
> https://gunkies.org/wiki/PDP-11/23#:~:text=hampage.hu,are%20no%20problems%20with%20this.
> 
> 
> To your questions. Because it lacks separate I/D
> Space and does not support supervisor mode (only user and kernel) 2.11BSD
> will not work.  However V6 and V7 are possible. I think Ultrix-11 should be
> able to work and is more likely to have the low level details that 11/23
> will need.
> 
> 
> Sent from a handheld expect more typos than usual
> 
> 
>> On Thu, Feb 26, 2026 at 5:52 PM ROBERT MYERS via TUHS <tuhs@tuhs.org> wrote:
>> 
>> I’ve just obtained a 11/23 Plus system off of EBay and plan to get a QBone
>> to emulate memory along with a few other things.  I need to know if
>> Floating Point support is a requirement as well if I can also emulate up to
>> 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
>> Sent from my iPhone
>> 

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

[segaloco via TUHS]

On Thursday, February 26th, 2026 at 15:06, Madeline Autumn-Rose via TUHS <tuhs@tuhs.org> wrote:

> v7m is also an option
> Sent from my iPhone
> 
> > On Feb 26, 2026, at 15:03, Clem Cole via TUHS <tuhs@tuhs.org> wrote:
> >
> > https://gunkies.org/wiki/PDP-11/23#:~:text=hampage.hu,are%20no%20problems%20with%20this.
> >
> >
> > To your questions. Because it lacks separate I/D
> > Space and does not support supervisor mode (only user and kernel) 2.11BSD
> > will not work.  However V6 and V7 are possible. I think Ultrix-11 should be
> > able to work and is more likely to have the low level details that 11/23
> > will need.
> >
> >
> > Sent from a handheld expect more typos than usual
> >
> >
> >> On Thu, Feb 26, 2026 at 5:52 PM ROBERT MYERS via TUHS <tuhs@tuhs.org> wrote:
> >>
> >> I’ve just obtained a 11/23 Plus system off of EBay and plan to get a QBone
> >> to emulate memory along with a few other things.  I need to know if
> >> Floating Point support is a requirement as well if I can also emulate up to
> >> 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
> >> Sent from my iPhone
> >>
> 
>

Here is a salient document:

https://www.tuhs.org/Archive/Documentation/Manuals/Unix_4.0/Volume_2/F.5.3_UNIX_on_the_PDP_11_34.pdf

Therein Ted Kowalski describes the process of moving UNIX from the
PDP-11/70 to the PDP-11/34, with mentions of the PDP-11/23 also being a
beneficiary of the porting efforts.  If there's not an out-of-the-box
solution already, this paper may be useful in re-porting V6, as would be
referring to Mini-UNIX and LSX, both of which are in the UNIX tree.

- Matt G.

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

[Jay Logue via TUHS]

As others have said, 2.9BSD will run, but 2.11 wont.

Check out the 2.9BSD-MSCP.txt file in this directory: 
https://www.tuhs.org/Archive/Distributions/UCB/2.9-derivatives/2.9BSD-MSCP/

--Jay

On 2/26/26 14:52, ROBERT MYERS via TUHS wrote:
> I’ve just obtained a 11/23 Plus system off of EBay and plan to get a QBone to emulate memory along with a few other things.  I need to know if Floating Point support is a requirement as well if I can also emulate up to 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
> Sent from my iPhone

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

[Clem Cole via TUHS]

Absolutely.  v7m was the precursor to both Ultrix-11 and 2.9BSD [2.10BSD
took from Ultrix-11, while 2.8 and 2.9, v7m]. You can even see the emails
from DEC giving the Berkeley team to use anything from either

I suggested Ultrix-11 as I know it has simple (binary) installation media
readily available that supports the 11/23 [sources are also on TUHS].  But
unlike V7m, it was a standard product (supported by DEC at the time)
packaged appropriately  and included a number of enhancements (ie it was a
DEC product and you can even download a PDF of it’s official software
product description (SPD) - which is the official document that described
what DEC would provide support.


v7m was basically a tape distribution by DEC made available to Unix V7
licensees ( and followed the ATT “abandoned on your doorstep” style of
license).  But yes, it supports more models of PDP-11 than the original
Seventh Edition but trying to get it running on real hardware will take
more effort.


Sent from a handheld expect more typos than usual


On Thu, Feb 26, 2026 at 6:06 PM Madeline Autumn-Rose <b4@gewt.net> wrote:

> v7m is also an option
> Sent from my iPhone
>
> > On Feb 26, 2026, at 15:03, Clem Cole via TUHS <tuhs@tuhs.org> wrote:
> >
> > 
> https://gunkies.org/wiki/PDP-11/23#:~:text=hampage.hu,are%20no%20problems%20with%20this
> .
> >
> >
> > To your questions. Because it lacks separate I/D
> > Space and does not support supervisor mode (only user and kernel) 2.11BSD
> > will not work.  However V6 and V7 are possible. I think Ultrix-11 should
> be
> > able to work and is more likely to have the low level details that 11/23
> > will need.
> >
> >
> > Sent from a handheld expect more typos than usual
> >
> >
> >> On Thu, Feb 26, 2026 at 5:52 PM ROBERT MYERS via TUHS <tuhs@tuhs.org>
> wrote:
> >>
> >> I’ve just obtained a 11/23 Plus system off of EBay and plan to get a
> QBone
> >> to emulate memory along with a few other things.  I need to know if
> >> Floating Point support is a requirement as well if I can also emulate
> up to
> >> 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
> >> Sent from my iPhone
> >>
>
>

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

[ROBERT MYERS via TUHS]

Can Mini-Uniz run on a 11/23 Plus?  I know it runs on a 11/40.

> On Feb 26, 2026, at 5:19 PM, segaloco via TUHS <tuhs@tuhs.org> wrote:
> 
> On Thursday, February 26th, 2026 at 15:06, Madeline Autumn-Rose via TUHS <tuhs@tuhs.org> wrote:
> 
>> v7m is also an option
>> Sent from my iPhone
>> 
>>> On Feb 26, 2026, at 15:03, Clem Cole via TUHS <tuhs@tuhs.org> wrote:
>>> 
>>> https://gunkies.org/wiki/PDP-11/23#:~:text=hampage.hu,are%20no%20problems%20with%20this.
>>> 
>>> 
>>> To your questions. Because it lacks separate I/D
>>> Space and does not support supervisor mode (only user and kernel) 2.11BSD
>>> will not work.  However V6 and V7 are possible. I think Ultrix-11 should be
>>> able to work and is more likely to have the low level details that 11/23
>>> will need.
>>> 
>>> 
>>> Sent from a handheld expect more typos than usual
>>> 
>>> 
>>>> On Thu, Feb 26, 2026 at 5:52 PM ROBERT MYERS via TUHS <tuhs@tuhs.org> wrote:
>>>> 
>>>> I’ve just obtained a 11/23 Plus system off of EBay and plan to get a QBone
>>>> to emulate memory along with a few other things.  I need to know if
>>>> Floating Point support is a requirement as well if I can also emulate up to
>>>> 4 Mb of memory.  I’m interested in v6/v7/BSD2.11 for Unix variants.
>>>> Sent from my iPhone
>>>> 
>> 
>> 
> 
> Here is a salient document:
> 
> https://www.tuhs.org/Archive/Documentation/Manuals/Unix_4.0/Volume_2/F.5.3_UNIX_on_the_PDP_11_34.pdf
> 
> Therein Ted Kowalski describes the process of moving UNIX from the
> PDP-11/70 to the PDP-11/34, with mentions of the PDP-11/23 also being a
> beneficiary of the porting efforts.  If there's not an out-of-the-box
> solution already, this paper may be useful in re-porting V6, as would be
> referring to Mini-UNIX and LSX, both of which are in the UNIX tree.
> 
> - Matt G.

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

[Noel Chiappa via TUHS]

    > From: Matt Gilmore

    > If there's not an out-of-the-box solution already, this paper may be
    > useful in re-porting V6

Not quite "out-of-the-box", but there are detailed instructions on how to
bring up V6 on a /23:

  https://gunkies.org/wiki/Running_UNIX_V6_on_an_-11/23

That page was prepared after actually doing it on actual hardware, so there
are no not-yet-seen tarpits (note the reference to "has been observed to
trash the disk, if you are really unlucky").

I suspect the biggest obstacle is likely to be getting the bits onto whatever
the OP is using for mass storage (I see a reference to "QBone to emulate
memory", but whether "memory" there refers to 'main memory' or 'mass storage'
I'm not clear on, although the later "emulate up to 4 Mb of memory" makes me
think the former might have been meant; I'm not familiar with the QBone).

You do need the KTF11-A memory management chip to run anything other than
MINI-UNIX or LSX, but I think all -11/23 Plus systems have it.


    >> I need to know if Floating Point support is a requirement as well

Not required; "if it has a KEF11-A floating point chip, [a small amount of ]
additional work is needed to allow its general use, since the -11/40 did not
support FP11 floating point, and so there is no code to handle it in m40.s."

    "if I can also emulate up to 4 Mb of memory

"All -11/23's after the (very rare) model A can support more than 256KB of
main memory. If you put more than 256KB on an -11/23 and boot V6, it will
ignore the extra memory above 256KB (technically, above 248KB)." but it's
simple to allow use of more (see the instructions, for how).


    > From: Robert Myers

    > Can Mini-Uniz run on a 11/23 Plus?

It should; I got it to run on an -11/03. See:

  http://ana-3.lcs.mit.edu/~jnc/tech/unix/Mini/Mini.html

but there's no point if you hsve a KTF11-A.

	Noel

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

[Noel Chiappa via TUHS]

    > From: Matt Gilmore

    > Here is a salient document:

    > Therein Ted Kowalski describes the process of moving UNIX from the
    > PDP-11/70 to the PDP-11/34

Why he started with the /70 version, which is a far way more complicated than
the /23 & /34, instead of the already extant /40 version, which is almost
exactly what one needs for the /23 & /34, is completely unclear to me.

The /40 uses the same memory management as that supported by the /23 (the
'simple' kind, i.e. without split I+D and Supervisor mode).

	Noel

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

[Ron Natalie via TUHS]

I was responsible for bringing up UNIX on an 11/23.    It was a long 
time ago, but this system replaced an existing lsi11 (11/03) that was 
already running miniUNIX, so I almost certainly used that to fill in the 
initial root image.   We were already running a full up V6 UNIX on the 
11/45 downstairs, so I could shuffle things around pretty easily.   I 
suspect all the machines had RK05 controllers.

Amusingly, we had built our own little console switch that let us switch 
things from system to system.    Once we got UNIX up on the lab 
computer, we messed with one of the grad students by switching him back 
and forth between the two machines until he caught on.




------ Original Message ------
From "Noel Chiappa via TUHS" <tuhs@tuhs.org>
To tuhs@tuhs.org
Cc jnc@mercury.lcs.mit.edu
Date 2/27/2026 09:37:26
Subject [TUHS] Re: Can PDP-11/23 PLUS run Unix?

>     > From: Matt Gilmore
>
>     > If there's not an out-of-the-box solution already, this paper may be
>     > useful in re-porting V6
>
>Not quite "out-of-the-box", but there are detailed instructions on how to
>bring up V6 on a /23:
>
>https://gunkies.org/wiki/Running_UNIX_V6_on_an_-11/23
>
>That page was prepared after actually doing it on actual hardware, so there
>are no not-yet-seen tarpits (note the reference to "has been observed to
>trash the disk, if you are really unlucky").
>
>I suspect the biggest obstacle is likely to be getting the bits onto whatever
>the OP is using for mass storage (I see a reference to "QBone to emulate
>memory", but whether "memory" there refers to 'main memory' or 'mass storage'
>I'm not clear on, although the later "emulate up to 4 Mb of memory" makes me
>think the former might have been meant; I'm not familiar with the QBone).
>
>You do need the KTF11-A memory management chip to run anything other than
>MINI-UNIX or LSX, but I think all -11/23 Plus systems have it.
>
>
>     >> I need to know if Floating Point support is a requirement as well
>
>Not required; "if it has a KEF11-A floating point chip, [a small amount of ]
>additional work is needed to allow its general use, since the -11/40 did not
>support FP11 floating point, and so there is no code to handle it in m40.s."
>
>     "if I can also emulate up to 4 Mb of memory
>
>"All -11/23's after the (very rare) model A can support more than 256KB of
>main memory. If you put more than 256KB on an -11/23 and boot V6, it will
>ignore the extra memory above 256KB (technically, above 248KB)." but it's
>simple to allow use of more (see the instructions, for how).
>
>
>     > From: Robert Myers
>
>     > Can Mini-Uniz run on a 11/23 Plus?
>
>It should; I got it to run on an -11/03. See:
>
>http://ana-3.lcs.mit.edu/~jnc/tech/unix/Mini/Mini.html
>
>but there's no point if you hsve a KTF11-A.
>
>	Noel

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

[Ron Natalie via TUHS]

There’s not really anything much different across the lines on the 
PDP-11 kernels.   We ran essentially the same source base on the 11/23, 
24, 40 (if it had memory management), 34, 45, and 70.    The 24, 45, and 
70 had split I/D and the early V6s would run on any, but once we built 
our kernels for split I/D, we couldn’t run them on the 34s we had.   The 
70 could address more memory (as did the 24).     When the kernels 
started getting larger, we ended up having to put overlays on the 
non-split machines.   The death of them were when we needed an 
additional segment register to map the BSDish mbufs for the TCP code.   
At that point, all the non-split I/D machines were recycled into various 
utility roles (mostly internet routers, but also as an I/O controller 
for the HEP).   The UNIX kernel was replaced with my Little Operating 
System (No time for sharing) that I used tor place Noel’s MIT C gateway 
as it had some limitations and Noel had been exiled to the Bahamas or 
something while we were trying to get things running.

Eventually, even the 70s got too small for the jobs needed and they got 
recycled into routers as well.    An 11/70 is sort of overkill for this, 
but I had them for free.

I have fond memories of my years on the PDP-11 and those early UNIXes.   
  I remember when they finally got the PDP-11 down to a single chip 
(T11).   Of course, the DEC guy doing the marketing says “it has the 
full instruction set other than the MARK instruction.”   Me and one 
other geek are going “What?   No mark instruction?”    This instruction 
is about the most useless thing in the world.

------ Original Message ------
From "Noel Chiappa via TUHS" <tuhs@tuhs.org>
To tuhs@tuhs.org
Cc jnc@mercury.lcs.mit.edu
Date 2/27/2026 09:50:28
Subject [TUHS] Re: Can PDP-11/23 PLUS run Unix?

>     > From: Matt Gilmore
>
>     > Here is a salient document:
>
>     > Therein Ted Kowalski describes the process of moving UNIX from the
>     > PDP-11/70 to the PDP-11/34
>
>Why he started with the /70 version, which is a far way more complicated than
>the /23 & /34, instead of the already extant /40 version, which is almost
>exactly what one needs for the /23 & /34, is completely unclear to me.
>
>The /40 uses the same memory management as that supported by the /23 (the
>'simple' kind, i.e. without split I+D and Supervisor mode).
>
>	Noel

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

[Clem Cole via TUHS]

Below

On Fri, Feb 27, 2026 at 8:50 AM Noel Chiappa via TUHS <tuhs@tuhs.org> wrote:

>     > From: Matt Gilmore
>
>     > Here is a salient document:
>
>     > Therein Ted Kowalski describes the process of moving UNIX from the
>     > PDP-11/70 to the PDP-11/34
>
> Why he started with the /70 version, which is a far way more complicated
> than
> the /23 & /34, instead of the already extant /40 version, which is almost
> exactly what one needs for the /23 & /34, is completely unclear to me.
>
He didn't actually.   About 6 months before Ted arrived at CMU for his OYIC
master's time[IIRC Wayne Gramlich and Danny Klien had fingers in that pot
too], I worked on the 11/34 port of V6 to the 11/34.  We started with the
11/40 version and changed a few things that differed between the 40 and 34
(CMU-EE/CS did not have an 11/23 in the mid/late '70s).   Ted brought with
him the V6++/TS bits from USG.  We switched to his kernel and already had
his USG-based system running. [I think I have an archive of that system].


I believe he wrote that document in 1981 for USG release of Unix 4.0, as
documentation on the differences.

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

[Noel Chiappa via TUHS]

    > From: Clem Cole

    >> Why he started with the /70 version .. instead of the already extant
    >> /40 version

    > He didn't actually. 

The paper spends a lot of space, in Section 2.2 'Instruction Backup',
describing how to do instruction backup. Section 3 'Implementation of
PDP-11/34 UNIX' is not clear if he re-wrote that stuff; it lists "fault
handling" as something he did write (which could include instruction backup,
but might not). Instruction backup on machines without an MMR1 (like the /34)
was fully supported as of V5 (which supported the /40). Why all the attention
to instruction backup, if it was already done?


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

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

[Al Kossow via TUHS]

On 2/27/26 1:48 PM, Noel Chiappa via TUHS 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
> 

I was wondering why no one was mentioning 2.9 as something that
could be run on an F11

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

[Clem Cole via TUHS]

below..

On Fri, Feb 27, 2026 at 4:48 PM Noel Chiappa via TUHS <tuhs@tuhs.org> wrote:

>  Why all the attention to instruction backup, if it was already done?
>
I have no idea. And sadly, we can not ask him.  We lost him several years
ago to cancer.   I tried to get Lisa (his widow) to let me review his
collection of technology, but she wouldn't allow it, and I believe some
treasures have been lost.  I know he had some stuff from CMU (such as his
ISPS system, which he developed for his PhD).

>
> 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:
>
Actually, it came from v7m.  Fred Cantor wrote it.  Bostic and the 2. X
crew pulled it from v7m.

v7m and 2.XBSD can run on both Unibus and QBUS PDP-11s, but as I said, the
F-11 lacks a separate I/D Space and does not support supervisor mode (only
user and kernel), so 2.11BSD will not work.

It's a matter of taste and effort between Ultrix-11 and 2.9BSD.  If you
have a Unibone or a Qbone, thern its easy to use simh to create the proper
disk images.   Then load them into the SSD on the Unibone/QBone.   A while
back, I helped Dave Plummer with getting his PDP-11/83 running with 2.11BSD
using this scheme.

Clem

[TUHS] Re: 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

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

[Noel Chiappa via TUHS]

    > From: Phil Budne

    > V7M has overlays

Ah, the CHWiki doesn't have a page for that system; I'll have to add it.

Yes, it does seem to have had _kernel_ overlays before 2.9 (I looked, to see
if I could find any direct credit in 2.9, to indicate that their support for
kernel overlays came from V7M, but couldn't; I'm too lazy to do sources
compares).

I say "_kernel_ overlays" because I gather (see some evidence, below) that
use-of/support-for overlays in _processes_, in user mode, preceded
use-of/support-for overlays in the kernel.

See:

  "Running Large Text Processes on Small Unix Systems", Charles Haley,
  William Joy, William F. Jolitz
  https://www.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/doc/ovpap

  "We describe a set of simple modifications to the Unix system, which permit
  larger programs to be run than has previously been possible. In particular,
  the 'f77' and 'a68' compilers and version 2 of the 'ex' editor, which
  previously would not run on the non-separate I/D machines such as the
  11/23, 11/34 and 11/40, may be run, without source code modification, using
  this scheme. This scheme will also allow processes larger than 65K bytes of
  instruction space to run on all 11/ cpu's with segmentation hardware.

and:

  "How to use the UNIX Automatic Text Overlays: A Tutorial", Barbara Bekins,
  Bill Jolitz
  https://www.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/doc/ovtutorial

The former unfortunately does not have a date on it; the latter has a date of
10/20/81, but we can infer that the original work was before that. It does
appear to be later than "The Second BSD" (1979-04); there's nothing about
overlats that I could find there..


V7M contains notes that more or less state that its use-of/support-for
overlays in the kernel is based on the prior support for overlays in
_processes_, done at Berkeley:

  This directory contains the C overlay loader and some other junk. ... Covld
  is derived from Bill Joy's covld .. The paper in ovpap.n describes the
  original Berkeley overlayed text scheme which was intended for use in user
  mode programs. I use overlays only for the kernel itself.

  https://www.tuhs.org/cgi-bin/utree.pl?file=V7M/src/cmd/covld/README


I also have a memory that someone did some work that allowed large amounts of
disk buffers (and maybe clists too), which were not statically mapped into
kernel address space; one segment was used to map them in, as needed.

Can anyone point me at anything which covers that? (URL's would be a big plus!)
I will add all that (and this) to the appropriate places in the CHWiki.


I understand that all these kludges were not really important; in the long run,
they were dead ends. I just want to see them all documented, and credit
correctly assigned (as above, for the code overlays).

	Noel