VAX PDP11 Compatibility Mode

[David Wade]

Folks,

I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this was
no longer needed.

I also see from the VAX Architecture Reference manual from bitsavers

EY-3459E-DP_VAX_Architecture_Reference_Manual_1987

that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.

... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.

So my questions are:-

1. Is there a matrix somewhere that shows which models of VAX have which
feature, especially the PDP11 compatibility mode.

2. Did any versions of VMS implement software emulation of the PDP11

3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a PDP11
executable?

I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.

Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...

Dave

[Jan-Erik Söderholm]

Post by David Wade
Folks,
 I remember being taught on an Introduction to VMS course that whilst VMS
versions prior to 4.0 relied on PDP-11 compatibility mode, this was no
longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference to
PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have which
feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11

$ mcr
%DCL-W-ACTIMAGE, error activating image RSX
-CLI-E-IMAGEFNF, image file not found $1$DKA0:[SYS0.SYSCOMMON.][SYSEXE]RSX.EXE;
$

I would guess that this (missing) RSX.EXE has something to do
with the PDP11 emulation...

Post by David Wade
3. If you have an old VMS and an old VAX how did you invoke compatibility
mode? Was there a flag in the file to show it was a PDP11 executable?
I have tried googling but the results get so entangled with VAX and PDP11
emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other things.
Some one mentioned this on the CCTALK list so it re-kindled my curiosity..
Thanks for any replies...
Dave

[Jeffrey H. Coffield]

Post by Jan-Erik Söderholm

Post by David Wade
Folks,
I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this
was no longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have
which feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11

$ mcr
%DCL-W-ACTIMAGE, error activating image RSX
-CLI-E-IMAGEFNF, image file not found
$1$DKA0:[SYS0.SYSCOMMON.][SYSEXE]RSX.EXE;
$
I would guess that this (missing) RSX.EXE has something to do
with the PDP11 emulation...

Post by David Wade
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a
PDP11 executable?
I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...
Dave

Try this:

https://comp.os.vms.narkive.com/N4yPsEEV/a-simple-question-what-the-h-ll-is-mcr

Jeff C.

[David Wade]

Post by Jeffrey H. Coffield

Post by Jan-Erik Söderholm

Post by David Wade
Folks,
  I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this
was no longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have
which feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11

$ mcr
%DCL-W-ACTIMAGE, error activating image RSX
-CLI-E-IMAGEFNF, image file not found
$1$DKA0:[SYS0.SYSCOMMON.][SYSEXE]RSX.EXE;
$
I would guess that this (missing) RSX.EXE has something to do
with the PDP11 emulation...

Post by David Wade
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a
PDP11 executable?
I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...
Dave

https://comp.os.vms.narkive.com/N4yPsEEV/a-simple-question-what-the-h-ll-is-mcr
Jeff C.

interesting thread which implies its a VMS feature but I can see it
documented in the manuals. Time for some more searching...

.. and thanks for all the replies. Very interesting..

Dave

[Bob Koehler]

Post by David Wade
interesting thread which implies its a VMS feature but I can see it
documented in the manuals. Time for some more searching...
.. and thanks for all the replies. Very interesting..

The obsolete Obsolete Features Manual?

Or a VMS 2.x doc set.

[Bob Gezelter]

Post by David Wade
Folks,
I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this was
no longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have which
feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a PDP11
executable?
I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...
Dave

Dave,

Early VAX processors had hardware/firmware support for PDP-11 compatibility mode. The systems software component of the support was the RSX-11 Applications Migration Executive (AME).

Early versions of VAX/VMS took advantage of this support. Ar first ship, many utilities and compilers ran in compatibility mode (e.g., PIP, FORTRAN, and others).

If memory serves, the MicroVAX was the first VAX without PDP-11 support. At that point, the RSX-11 AME was repackaged as an optional layered product, including software emulation of the PDP-11 non-privileged instruction set.

RSX-11 and VAX executables have different headers, and can be distinguished. My recollection is that this is described in the image activation section of the IDSM.

- Bob Gezelter, http://www.rlgsc.com

[Lee Gleason]

Post by David Wade
3. If you have an old VMS and an old VAX how did you invoke compatibility
mode? Was there a flag in the file to show it was a PDP11 executable?

At the lowest level, it is invoked by doing an REI when you have the
compatibility mode bit set in the PSL that is on the stack. PSL bits
FPD,ISPL,IV, FU and DV must be 0. CURMOD and PRVMOD must be 3.

It is exited when an interrupt or exception occurs.

--
Lee K. Gleason N5ZMR
Control-G Consultants
***@comcast.net

[Chris Scheers]

Post by David Wade
Folks,
I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this was
no longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have which
feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a PDP11
executable?
I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...

That description is a bit backwards. It wasn't that compatibility mode
was no longer needed. It was that VMS 4.0 was meant to support the new
MicroVAX models, which did not have compatibility mode. So any VMS
utilities that used compatibility mode had to be rewritten as VAX code
for VMS 4.0.

IIRC, the models that supported PDP-11 compatibility mode were: 730,
750, 780, 785, 8600.

I never used it, but for VMS 4.0 there was a layered product that
activated the MCR function for compatibility mode. I don't know if it
just allowed execution on hardware that had compatibility mode or if it
included an emulator.

[Bob Gezelter]

Post by Chris Scheers

Post by David Wade
Folks,
I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this was
no longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have which
feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a PDP11
executable?
I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...

That description is a bit backwards. It wasn't that compatibility mode
was no longer needed. It was that VMS 4.0 was meant to support the new
MicroVAX models, which did not have compatibility mode. So any VMS
utilities that used compatibility mode had to be rewritten as VAX code
for VMS 4.0.
IIRC, the models that supported PDP-11 compatibility mode were: 730,
750, 780, 785, 8600.
I never used it, but for VMS 4.0 there was a layered product that
activated the MCR function for compatibility mode. I don't know if it
just allowed execution on hardware that had compatibility mode or if it
included an emulator.
--
-----------------------------------------------------------------------
Chris Scheers, Applied Synergy, Inc.
Fax: [phone]

Chris,

The RSX-11 AME definitely included the emulator.

At a client site, I had the RSX-11 FORTRAN-77 compiler hosted on a MicroVAX 2000, cross-compiling for a J-11-based system.

One has to be careful referring to "MCR" on OpenVMS. It refers to the MCR CLI, which as I recall is part of the AME package. However, it is also a shorthand for SYS$SYSTEM:, as in MCR AUTHORIZE.

- Bob Gezelter, http://www.rlgsc.com

[John Reagan]

Post by Bob Gezelter

Post by Chris Scheers

Post by David Wade
Folks,
I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this was
no longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have which
feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a PDP11
executable?
I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...

That description is a bit backwards. It wasn't that compatibility mode
was no longer needed. It was that VMS 4.0 was meant to support the new
MicroVAX models, which did not have compatibility mode. So any VMS
utilities that used compatibility mode had to be rewritten as VAX code
for VMS 4.0.
IIRC, the models that supported PDP-11 compatibility mode were: 730,
750, 780, 785, 8600.
I never used it, but for VMS 4.0 there was a layered product that
activated the MCR function for compatibility mode. I don't know if it
just allowed execution on hardware that had compatibility mode or if it
included an emulator.
--
-----------------------------------------------------------------------
Chris Scheers, Applied Synergy, Inc.
Fax: [phone]

Chris,
The RSX-11 AME definitely included the emulator.
At a client site, I had the RSX-11 FORTRAN-77 compiler hosted on a MicroVAX 2000, cross-compiling for a J-11-based system.
One has to be careful referring to "MCR" on OpenVMS. It refers to the MCR CLI, which as I recall is part of the AME package. However, it is also a shorthand for SYS$SYSTEM:, as in MCR AUTHORIZE.
- Bob Gezelter, http://www.rlgsc.com

More than that, the parameter processing is more like a foreign command.

You cannot do

$ run sys$system:authorize show jreagan

but you can do

$ mcr authorize show jreagan

[Bill Gunshannon]

Post by David Wade
Folks,
 I remember being taught on an Introduction to VMS course that whilst
VMS versions prior to 4.0 relied on PDP-11 compatibility mode, this
was no longer needed.
I also see from the VAX Architecture Reference manual from bitsavers
EY-3459E-DP_VAX_Architecture_Reference_Manual_1987
that PDP11 emulation is an optional feature, and that it may also be
implemented by software for systems which did not have it.
... but looking through the OpenVMS manuals I can't find any reference
to PDP-11 compatibility mode.
So my questions are:-
1. Is there a matrix somewhere that shows which models of VAX have
which feature, especially the PDP11 compatibility mode.
2. Did any versions of VMS implement software emulation of the PDP11
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a
PDP11 executable?
I have tried googling but the results get so entangled with VAX and
PDP11 emulation pages its hard to drill down to the real info.
Also sorry for the historicial question. This is something I have long
wanted to know the answers too, but have been distracted by other
things. Some one mentioned this on the CCTALK list so it re-kindled my
curiosity.. Thanks for any replies...

That description is a bit backwards.  It wasn't that compatibility mode
was no longer needed.  It was that VMS 4.0 was meant to support the new
MicroVAX models, which did not have compatibility mode.  So any VMS
utilities that used compatibility mode had to be rewritten as VAX code
for VMS 4.0.
IIRC, the models that supported PDP-11 compatibility mode were: 730,
750, 780, 785, 8600.
I never used it, but for VMS 4.0 there was a layered product that
activated the MCR function for compatibility mode.  I don't know if it
just allowed execution on hardware that had compatibility mode or if it
included an emulator.

Hmmm.... Is this the origin of the original Bob Supnik PDP-11
emulator? It would certainly explain the Paragraph in the Mentec
license that requires :

"software owned by Digital Equipment Corporation
that emulates the operation of a PDP-11 processor
and allows PDP-11 programs and operating systems
to run on non-PDP-11 systems"

which people have always tried to claim meant SIMH.

bill

[Terry Kennedy]

Post by Chris Scheers
That description is a bit backwards. It wasn't that compatibility mode
was no longer needed. It was that VMS 4.0 was meant to support the new
MicroVAX models, which did not have compatibility mode. So any VMS
utilities that used compatibility mode had to be rewritten as VAX code
for VMS 4.0.

By the time the uV II and 86xx had come out, enough instruction traces had been gathered to prove the general "10% of the code is used 90% of the time" and a number of instruction subsets had been investigated, with microcode assist for VAX code implementation of the missing instructions.

That is also what caused (mostly*) the PDP-11 CIS options (11/23, 11/24, 11/44) to get dropped on later models - they implemented a superset of the VAX string, packed decimal, etc. instructions which were some of the first to be thrown overboard when the VAX architecture was subsetted. I think there's a couple of those instructions that were used frequently enough that they were retained even in the subsets.

* The late / slow / buggy nature of the J-11 chipset also didn't help. There were provisions for CIS microms on the underside of the ceramic carrier. But it seems DEC was "happy" enough to get chips that worked (although not at the original design speed**) that they abandoned CIS for both implementation difficulty and lack of usefulness reasons.

** The original top bin was 5Mhz with a 20MHz crystal. The fastest "official" J-11 speed was 18MHz. The support chipset DEC used didn't work*** at 20MHz, so that was dropped as a product goal. The PDP-11/93 and /94 CPU board (designed by ROI, sold by DEC) didn't use the DEC support chipset and didn't have those limitations. My "Report from the field (test)" DECUS Symposium presentation (arranged by DEC, not some massive non-disclosure violation by me) originally had benchmark results at 20, 24 and 26MHz (28MHz was flakey) but when I ran it by DEC I was politely asked to remove those if I didn't mind.

*** This was when PDP-11 related semiconductor fab was getting squeezed by VAX designs in the pipeline, leading to a raft of "it's broke, but we'll ship it anyway" silicon. The 2MB PMI memory board that didn't work in one of Unibus or Q-bus (I forget which) was another example that needed to wait a long time for fixed chips.

Post by Chris Scheers
IIRC, the models that supported PDP-11 compatibility mode were: 730,
750, 780, 785, 8600.

All 7xx, 8600/8650 had hardware compatibility mode.

Post by Chris Scheers
I never used it, but for VMS 4.0 there was a layered product that
activated the MCR function for compatibility mode. I don't know if it
just allowed execution on hardware that had compatibility mode or if it
included an emulator.

Trivia - TECO was not rewritten in VAX assembler, so it carried its own PDP-11 support (or there was a magic exemption for it in the AME licensing, I forget which but think it was the former).

VSI folks might know if Itanium TECO is on Itanium emulating Alpha emulating VAX emulating PDP-11 8-}

[Michael Moroney]

Terry Kennedy <terry-***@glaver.org> writes:

Interesting about the J11. That's where I started, and I knew there were "issues"
but not what they were, other than the original planned 20 MHz clock.

Post by Terry Kennedy

Post by Chris Scheers
IIRC, the models that supported PDP-11 compatibility mode were: 730,
750, 780, 785, 8600.

All 7xx, 8600/8650 had hardware compatibility mode.

The 7xx series technically included the 8600. It was originally to be the
790.

I don't think the 8650 ever had a 7xx number, unlikely. If it did, I'd guess it
would be the VAX 795.

Post by Terry Kennedy
Trivia - TECO was not rewritten in VAX assembler, so it carried its own PDP-11
support (or there was a magic exemption for it in the AME licensing, I
forget which but think it was the former).

No, there was a VAX TECO32 facility. Perhaps it was ported later, after everything
else was, but at some point it was ported to VAX.

Post by Terry Kennedy
VSI folks might know if Itanium TECO is on Itanium emulating Alpha emulating
VAX emulating PDP-11 8-}

The last step is false, the rest true.

Having X86 emulate Itanic emulating Alpha emulating VAX TECO is probably not in the
plans. :-)

[Dave Froble]

Post by Michael Moroney
Interesting about the J11. That's where I started, and I knew there were "issues"
but not what they were, other than the original planned 20 MHz clock.

Post by Terry Kennedy

Post by Chris Scheers
IIRC, the models that supported PDP-11 compatibility mode were: 730,
750, 780, 785, 8600.

All 7xx, 8600/8650 had hardware compatibility mode.

The 7xx series technically included the 8600. It was originally to be the
790.
I don't think the 8650 ever had a 7xx number, unlikely. If it did, I'd guess it
would be the VAX 795.

Post by Terry Kennedy
Trivia - TECO was not rewritten in VAX assembler, so it carried its own PDP-11
support (or there was a magic exemption for it in the AME licensing, I
forget which but think it was the former).

No, there was a VAX TECO32 facility. Perhaps it was ported later, after everything
else was, but at some point it was ported to VAX.

Post by Terry Kennedy
VSI folks might know if Itanium TECO is on Itanium emulating Alpha emulating
VAX emulating PDP-11 8-}

The last step is false, the rest true.
Having X86 emulate Itanic emulating Alpha emulating VAX TECO is probably not in the
plans. :-)

Would it not be more reasonable to have something on x86 emulate Alpha?
The VLW stuff on the itanic has got to be rather "foreign".

[Stephen Hoffman]

Post by Dave Froble
Would it not be more reasonable to have something on x86 emulate Alpha?
The VLW stuff on the itanic has got to be rather "foreign".

It'd probably be most reasonable to start with the existing TECO
rewrite presuming that works well enough, and avoid the layers of
translations.

The original TECO implementation on OpenVMS became a test of the image
translation tools.

Here, maybe use that TECO C rewrite, and contribute back—or fork and
publish—any changes and updates. The rewrite has a permissive license,
by all appearances.
http://almy.us/teco.html

Not sure about the license(s) for the TECO C updates and subsequent
platform ports, though. That'd likely require some discussions with
the folks involved, as I don't see a license listed.
https://github.com/blakemcbride/TECOC

TECO and EDT customizations for an IDE would be a modern expectation,
not that I'd expect that to become available in the near term.

[Tim Sneddon]

This post might be inappropriate. Click to display it.

[Stephen Hoffman]

On 2019-08-06 09:03:40 +0000, David Wade said:

Here's the VAX architecture standard: start reading:
https://archive.org/details/bitsavers_decvaxarch32Jan90_36555387

There are various (partial) collections of DEC standards and related
materials around, including:
https://manx-docs.org/collections/antonio/dec/standards/
http://decdoc.itsx.net/dec94mds/
http://www.mcmanis.com/chuck/computers/vaxen/

Post by David Wade
1. Is there a matrix somewhere that shows which models of VAX have
which feature, especially the PDP11 compatibility mode.

See DEC Standard 32—also known as DECSTD032—above. That's the
canonical description of a VAX, including describing some
never-released VAX designs.

The VAX-11 series systems have PDP-11 support in hardware. That's the
VAX-11/725, VAX-11/730, VAX-11/750, VAX-11/751, VAX-11/780, VAX-11/782
(ASMP), VAX-11/785, the largely-hypothetical and rarely-seen VAX-11/787
(ASMP), and the VAX-11/790 series that was released as the VAX 8600 and
a later upgrade was known as the VAX 8650 series.

VAX systems after the VAX-11 series do not have PDP-11 hardware
support, and these VAX systems have PDP-11 support via emulation.

The MicroVAX series was the first subset VAX, IIIRC. It had less than
what had been considered the full VAX instruction set. No MicroVAX had
PDP-11 hardware support.

Again, see DECSTD032, above.

Post by David Wade
2. Did any versions of VMS implement software emulation of the PDP11

VAX/VMS or OpenVMS itself? No. The RSX layered product did implement
that. There were some instruction emulations latent in OpenVMS, such
as VVIEF. Again, DECSTD032.

Post by David Wade
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a PDP11
executable?

The last of the V3.0 bits that were in compatibility mode included SYE
error formatter tool, and a few other giblets. V4.0 got rid of all of
those, and moved PDP-11 support into the aforementioned layered product.

The Monitor Console Routine command verb MCR was something that I was
working to remove from the OpenVMS documentation set years ago as the
choices there were to either document and support MCR, or to work to
expunge it from the documentation. MCR has some "interesting"
behaviors, too. Removing references to MCR and other related
references from the OpenVMS documentation happened when the particular
OpenVMS manual was "open" for changes, and which wasn't all that
often—if at all—for some of the OpenVMS manuals. Even back then. The
more actively-updated manuals got most (all?) of the references to MCR
expunged. No, there were no plans to remove the MCR command verb
itself. That was to be left latent. Just to deprecate it, save for
anyone that was still using the RSX compatibility mode product, or had
existing uses in their code. And as I've commented before, the OpenVMS
obsolete features manual was itself marked as obsolete. So there have
been no updates made there in many years. And IIRC, the removal of MCR
was after the obsolete-features manual was made obsolete.

[Jan-Erik Söderholm]

Post by Stephen Hoffman
https://archive.org/details/bitsavers_decvaxarch32Jan90_36555387
There are various (partial) collections of DEC standards and related
https://manx-docs.org/collections/antonio/dec/standards/
http://decdoc.itsx.net/dec94mds/
http://www.mcmanis.com/chuck/computers/vaxen/

Post by David Wade
1. Is there a matrix somewhere that shows which models of VAX have which
feature, especially the PDP11 compatibility mode.

See DEC Standard 32—also known as DECSTD032—above.  That's the canonical
description of a VAX, including describing some never-released VAX designs.
The VAX-11 series systems have PDP-11 support in hardware.  That's the
VAX-11/725, VAX-11/730, VAX-11/750, VAX-11/751, VAX-11/780, VAX-11/782
(ASMP), VAX-11/785, the largely-hypothetical and rarely-seen VAX-11/787
(ASMP), and the VAX-11/790 series that was released as the VAX 8600 and a
later upgrade was known as the VAX 8650 series.
VAX systems after the VAX-11 series do not have PDP-11 hardware support,
and these VAX systems have PDP-11 support via emulation.
The MicroVAX series was the first subset VAX, IIIRC.  It had less than what
had been considered the full VAX instruction set.  No MicroVAX had PDP-11
hardware support.
Again, see DECSTD032, above.

Post by David Wade
2. Did any versions of VMS implement software emulation of the PDP11

VAX/VMS or OpenVMS itself?  No.  The RSX layered product did implement
that.  There were some instruction emulations latent in OpenVMS, such as
VVIEF.  Again, DECSTD032.

Post by David Wade
3. If you have an old VMS and an old VAX how did you invoke compatibility
mode? Was there a flag in the file to show it was a PDP11 executable?

The last of the V3.0 bits that were in compatibility mode included SYE
error formatter tool, and a few other giblets.  V4.0 got rid of all of
those, and moved PDP-11 support into the aforementioned layered product.
The Monitor Console Routine command verb MCR was something that I was
working to remove from the OpenVMS documentation set years ago as the
choices there were to either document and support MCR, or to work to
expunge it from the documentation.  MCR has some "interesting" behaviors,
too.  Removing references to MCR and other related references from the
OpenVMS documentation happened when the particular OpenVMS manual was
"open" for changes, and which wasn't all that often—if at all—for some of
the OpenVMS manuals.  Even back then.  The more actively-updated manuals
got most (all?) of the references to MCR expunged.  No, there were no plans
to remove the MCR command verb itself. That was to be left latent...

I often use the MC command. Nice not to have symbols for all *CP.EXE
programs in SYS$SYSTEM. "MC LATCP SHOW ...", "MC LANCP SHOW ..." and
so on. Used if not daily so at least weekly...

[Stephen Hoffman]

Post by Jan-Erik Söderholm
I often use the MC command. Nice not to have symbols for all *CP.EXE
programs in SYS$SYSTEM. "MC LATCP SHOW ...", "MC LANCP SHOW ..." and so
on. Used if not daily so at least weekly...

Automatic foreign commands were to be (are) an approach that avoids MCR
for that sort of thing.

[David Wade]

Post by Stephen Hoffman
https://archive.org/details/bitsavers_decvaxarch32Jan90_36555387
There are various (partial) collections of DEC standards and related
https://manx-docs.org/collections/antonio/dec/standards/
http://decdoc.itsx.net/dec94mds/
http://www.mcmanis.com/chuck/computers/vaxen/

Post by David Wade
1. Is there a matrix somewhere that shows which models of VAX have
which feature, especially the PDP11 compatibility mode.

See DEC Standard 32—also known as DECSTD032—above.  That's the canonical
description of a VAX, including describing some never-released VAX designs.
The VAX-11 series systems have PDP-11 support in hardware.  That's the
VAX-11/725, VAX-11/730, VAX-11/750, VAX-11/751, VAX-11/780, VAX-11/782
(ASMP), VAX-11/785, the largely-hypothetical and rarely-seen VAX-11/787
(ASMP), and the VAX-11/790 series that was released as the VAX 8600 and
a later upgrade was known as the VAX 8650 series.
VAX systems after the VAX-11 series do not have PDP-11 hardware support,
and these VAX systems have PDP-11 support via emulation.
The MicroVAX series was the first subset VAX, IIIRC.  It had less than
what had been considered the full VAX instruction set.  No MicroVAX had
PDP-11 hardware support.
Again, see DECSTD032, above.

Post by David Wade
2. Did any versions of VMS implement software emulation of the PDP11

VAX/VMS or OpenVMS itself?  No.  The RSX layered product did implement
that.  There were some instruction emulations latent in OpenVMS, such as
VVIEF.  Again, DECSTD032.

Ok I will look at that. Meanwhile I found an SPD for VAX-11 RSX

http://h30266.www3.hpe.com/masterindex/spd/spd_0000f67f.txt

which states it uses emulation when compatibility mode is not available.

However the software is not on the distribution CDs I have. I wonder if
it was removed when MEMTEC bought the VAX...

Post by Stephen Hoffman

Post by David Wade
3. If you have an old VMS and an old VAX how did you invoke
compatibility mode? Was there a flag in the file to show it was a
PDP11 executable?

The last of the V3.0 bits that were in compatibility mode included SYE
error formatter tool, and a few other giblets.  V4.0 got rid of all of
those, and moved PDP-11 support into the aforementioned layered product.
The Monitor Console Routine command verb MCR was something that I was
working to remove from the OpenVMS documentation set years ago as the
choices there were to either document and support MCR, or to work to
expunge it from the documentation.  MCR has some "interesting"
behaviors, too.  Removing references to MCR and other related references
from the OpenVMS documentation happened when the particular OpenVMS
manual was "open" for changes, and which wasn't all that often—if at
all—for some of the OpenVMS manuals.  Even back then.  The more
actively-updated manuals got most (all?) of the references to MCR
expunged.  No, there were no plans to remove the MCR command verb
itself. That was to be left latent.  Just to deprecate it, save for
anyone that was still using the RSX compatibility mode product, or had
existing uses in their code.  And as I've commented before, the OpenVMS
obsolete features manual was itself marked as obsolete. So there have
been no updates made there in many years. And IIRC, the removal of MCR
was after the obsolete-features manual was made obsolete.

yes, its not in help or the 7.3 manuals but it seems to work as
advertised on VMS 7.3 under SIMH VAX emulation...

Dave

[Dennis Boone]

Post by David Wade
Ok I will look at that. Meanwhile I found an SPD for VAX-11 RSX
http://h30266.www3.hpe.com/masterindex/spd/spd_0000f67f.txt
which states it uses emulation when compatibility mode is not available.
However the software is not on the distribution CDs I have. I wonder if
it was removed when MEMTEC bought the VAX...

It's on the 5.5 CDs:

VAX-11 RSX 2.5 382AA 2 [RSX025]

De

[Dave Froble]

Post by David Wade
when MEMTEC bought the VAX...

Did I miss something? I was not aware that DEC or Compaq sold any parts
of the VAX.

[Bill Gunshannon]

Post by David Wade
when MEMTEC bought the VAX...

Did I miss something?  I was not aware that DEC or Compaq sold any parts
of the VAX.

They did not.

bill

[David Wade]

Post by David Wade
when MEMTEC bought the VAX...

Did I miss something?  I was not aware that DEC or Compaq sold any parts
of the VAX.

Sorry Dave. Not enough beer. When Memtec bought PDP-11...

Dave

[Stephen Hoffman]

Post by David Wade
Sorry Dave. Not enough beer. When Memtec bought PDP-11...

Mentec.

And the associated IP is reportedly now at XX2247.

[Bill Gunshannon]

Post by Stephen Hoffman

Post by David Wade
Sorry Dave. Not enough beer. When Memtec bought PDP-11...

Mentec.
And the associated IP is reportedly now at XX2247.

And appears to be even deader than it was at Mentec.

bill

[David Wade]

This post might be inappropriate. Click to display it.

[Bill Gunshannon]

Post by David Wade
However the software is not on the distribution CDs I have. I wonder if
it was removed when MEMTEC bought the VAX...

If you actually mean MENTEC, they never had anything to do with the
VAX. The VAX lived and died with Digital.

bill

[Dave Froble]

Post by Bill Gunshannon

Post by David Wade
However the software is not on the distribution CDs I have. I wonder
if it was removed when MEMTEC bought the VAX...

If you actually mean MENTEC, they never had anything to do with the
VAX. The VAX lived and died with Digital.
bill

Uh, who said it died? Got an old MicroVAX 3100 running on the table
here beside me.

:-)

[Bill Gunshannon]

Post by Bill Gunshannon

Post by David Wade
However the software is not on the distribution CDs I have. I wonder
if it was removed when MEMTEC bought the VAX...

If you actually mean MENTEC, they never had anything to do with the
VAX.  The VAX lived and died with Digital.
bill

Uh, who said it died?  Got an old MicroVAX 3100 running on the table
here beside me.
:-)

I have a half dozen of them running VMS, Ultrix and BSD. Doesn't
change the fact that the company that created and owned them has
died, the hardware is unobtanium (except in scrapyards), the OSes
have been on life support for more than a decade (actually, they
have all had the plug onthe life support pulled at this point)
for more than a decade, etc, etc, etc. Time to get a grip on
reality Dave. :-)

bill

[Dave Froble]

Post by Bill Gunshannon

Post by Dave Froble

Post by Bill Gunshannon

Post by David Wade
However the software is not on the distribution CDs I have. I wonder
if it was removed when MEMTEC bought the VAX...

If you actually mean MENTEC, they never had anything to do with the
VAX. The VAX lived and died with Digital.
bill

Uh, who said it died? Got an old MicroVAX 3100 running on the table
here beside me.
:-)

I have a half dozen of them running VMS, Ultrix and BSD. Doesn't
change the fact that the company that created and owned them has
died, the hardware is unobtanium (except in scrapyards), the OSes
have been on life support for more than a decade (actually, they
have all had the plug onthe life support pulled at this point)
for more than a decade, etc, etc, etc.

All true, but, as long as you're breathing, walking, talking, etc,
you're alive. Dead is when none of those can happen. Would you declare
your children dead, just cause you're too old to produce more?

Post by Bill Gunshannon
Time to get a grip on
reality Dave. :-)

Why would I ever want to do that? It's no fun. Without the "worlds of
if" things will never progress, get better, etc ....

[Jerry Eckert]

Here is some related trivia I did not see mentioned:

In early versions of VAX/VMS, the DCL file-related commands (e.g., DIR, COPY, RENAME, TYPE) invoked the image BACKTRANS.EXE that converted the DCL command into the equivalent PIP command and then chained to PIP in compatibility mode. BACKTRANS was used in V1 and V2; I don't recall if it was completely eliminated for V3.0.

Before BACKUP was implemented (I don't recall if it was in a late V2 release or in V3), the RSX utilities BCK and DSC (Disk Save and Compress) were used for online and standalone backups, respectively. I was working at the TSC at the time and, believe it or not, there were customers who refused to switch from BCK/DSC to BACKUP.

Jerry

[Jon Pinkley]

Post by Jerry Eckert
Before BACKUP was implemented (I don't recall if it was in a late V2 release or in V3), the RSX utilities BCK and DSC (Disk Save and Compress) were used for online and standalone backups, respectively. I was working at the TSC at the time and, believe it or not, there were customers who refused to switch from BCK/DSC to BACKUP.
Jerry

It's been so long since I used RSX I am not sure, but I thought the "online backup" utility was BRU (backu/restore utility). I don't remember a BCK, but that was a long time ago. I do remember using DSC on VAX/VMS, but I can't remember if it ever supported ODS2.

[Bob Gezelter]

Post by Jon Pinkley

Post by Jerry Eckert
Before BACKUP was implemented (I don't recall if it was in a late V2 release or in V3), the RSX utilities BCK and DSC (Disk Save and Compress) were used for online and standalone backups, respectively. I was working at the TSC at the time and, believe it or not, there were customers who refused to switch from BCK/DSC to BACKUP.
Jerry

It's been so long since I used RSX I am not sure, but I thought the "online backup" utility was BRU (backu/restore utility). I don't remember a BCK, but that was a long time ago. I do remember using DSC on VAX/VMS, but I can't remember if it ever supported ODS2.

Jon,

There were several iterations of backup utility.

The original was PRESERV, if I recall.

Then there was DSC (Disk save/compress), and finally BRU (Backup/Restore Utility). BRU could work with individual files.

If I recall correctly, DSC2 was the original VAX utility, working on a volume basis. BACKUP appeared later.

- Bob Gezelter, http://www.rlgsc.com

[Jon Pinkley]

Post by Bob Gezelter
Jon,
There were several iterations of backup utility.
The original was PRESERV, if I recall.
Then there was DSC (Disk save/compress), and finally BRU (Backup/Restore Utility). BRU could work with individual files.
If I recall correctly, DSC2 was the original VAX utility, working on a volume basis. BACKUP appeared later.
- Bob Gezelter, http://www.rlgsc.com

Bob,

You have a good memory. Found this about Disk Save and Compress Utility.

http://vaxhaven.com/images/2/26/AA-D739A-TE.pdf

There were two DSC programs, DSC1 (for ODS-1 disks) and the more often used DSC2 for ODS-2 disks. I remember booting the standalone DSC and backing up RP06 drives to a TU77 tape drive in 1980. I don't miss having to do that.

Things were much better after the BACKUP utility stabilized and we got a TU78.

I am reasonably sure that BACKUP was released in the with V3 or one of the V3 realeaes.

I first logged into a VAX in June of 1980, and I think it was V1.3 and we upgraded to V2 during the year end holidays.

Jon