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/
> 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.
> 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.
> 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.
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