15 Jul
2010
15 Jul
'10
6:01 p.m.
"Jerome H. Fine" <jhfinedp3k at compsys.to> wrote:
Huh? If you are suggesting that they would be the same, I can assure you
they could not.
A very common misconception these days seems to be that VAXen with PDP-1
compatibility could run PDP-11 programs. That is only true in a very
limited sense. Only the basic PDP-11 instruction set is supported by the
VAX, and only the user mode stuff. EMTs, as well as any other kind of
traps, interrupts, and so on, was *not* supported.
When you execute an EMT in PDP-11 mode on a VAX, it will trap back to
VAX mode. No possibility to have a PDP-11 trap handler.
Johnny
Billquist wrote:
> > >Ethan Dicks <ethan.dicks at
gmail.com> wrote:
>
>> >> >On 7/14/10, Jerome H. Fine <jhfinedp3k at compsys.to> wrote:
> >>
>> >>> In addition, does anyone know of any systems currently running
>> >>> which support RTEM-11 features which allow RT-11 programs
>> >>> to run in that environment? My assumption is that VMS on a VAX
>> >>> supported RTEM-11 at some point, but perhaps (if I am correct)
>> >>> the RTEM-11 support was not continued with
>> >>> more recent versions of VMS on the VAX and most definitely VMS on
the
>> >>> Alpha. Can anyone comment on these questions?
> >>
> >> Based on the vague reference at
> >> http://s-and-b.net/help?key=RTEM~Release_notes&title=VMS
Help&referer=
> >> and what I know of VMS and DEC hardware, I'd think that RTEM-11 would
> >> require a VAX processor with "compatibility mode", i.e., a
"VAX-11"
> >> processor. The primary models would be the 11/78x, 11/750, 11/730 and
> >> 11/725 (I don't recall if the VAX 86xx still had "compatibility
mode"
> >> or not, but it should be easy to check). MicroVAXen and such did not
> >> have it, and Alpha processors certainly did not have it.
> >>
> >> That being said, I have no experience with RTEM-11, but I would be
> >> surprised to learn it ran on a machine made after about 1986 or so.
>
> RTEM might be something else than RTEM-11, which was a software
> product for RSX. Just google for RTEM-11, and you'll find some
> references for it.
>
> However, I wonder about RTEM for VAX. It's certainly possible, but I
> can't find any other reference to it, and DEC's old SPDs, especially
> those with software version compatiblity matrixes, are usually pretty
> good as a way of finding out what software existed.
>
> As for PDP-11 compatibility in VAXen, yes, the 86x0 machines have
> that. Those were the last, however.
>
> For all other VAXen running VMS, if you wanted to run RSX software,
> you needed a PDP-11 emulator product for VMS, which was available, in
> addition to the RSX additions for VMS, which was also a separate
> product. That thing was supported up until fairly recently, though.
> But again, that's for RSX stuff...
I suspect that the most likely possibility is that RTEM and RTEM-11 are
used. In addition, I also suspect that both Johnny and Ethan
are correct in
that RTEM
was supported under both RSX and VMS on an older VAX which allowed
compatibility mode.
It would have to be totally separate products in that case.
I don''t know if Megan Gentry is still around
or perhaps Allison or one
of the
other DEC fellows. Perhaps they might at least know something about which
hardware and operating system(s) supported RTEM?
I definitely remember (and probably still have some mail somewhere) from
Megan mentioning that she used RTEM-11 for RT-11 work, running on RSX
machines. Possibly even an 11/74.
In addition, RSTS/E also supported RT-11 programs via
the SWITCH RT11
capability. However, only the RT-11 EMTs which are used by a SJ are
supported
by RSTS/E. At least there is quite reasonable documentation as well as
the ability
to test and actually run RT-11 programs under RSTS/E up to the latest
versions
of RSTS/E. RT-11 EMTs for mapped RT-11 monitors (RT11XM) are not supported
not are multi-terminal EMTs. Also, probably the latest RT-11 EMTs for
file status
information are also not supported under RSTS/E.
The correct technical term is that RSTS/E have a RT-11 *run time
system*. An RTS in RSTS/E provides an environment under which you can
get a specific behaviour. So you had RTSes for RT-11, RSX, BASIC+, TECO,
DCL and some other stuff. Some RTSes were also KBMs (keyboard monitors),
meaning you could "switch" to them, and get an interactive command line
interpreter with that. But the RTS mostly implemented system calls.
However, there were RTSes which didn't implement any system calls, and
only gave you the basic calls RSTS/E itself provided, and mostly focused
on being a KBM, such as DCL.
You can write you own RTS if you want to, and one think that have been
at the back of my mind is if it wouldn't be pretty easy to write a Unix
RTS for RSTS/E, so that you can run a bunch of Unix binaries under
RSTS/E as well.
All exeutable files have an RTS associated with it, and when the program
is run, it is run under that RTS, which then handles all EMTs and so on
when the program executes them.
Probably in the same manner as RSTS/E, if RTEM is
supported under VMS on an
older VAX, the most likely only the RT-11 EMTs which are used by a SJ are
supported.
Yes, RTEM-11 would most likely just provide a simple RT-11 environment,
such as SJ. As I said before, I can't really find any proper information
about any RT11 environment for VMS... But if it existed, it would
probably be just SJ as well.
Johnny