[Simh] VAX/VMS

Tue Feb 16 08:58:11 EST 2016

Dave be careful --   S/360 Model 67 has VM in the late 1960's - TSS and
it's brother MTS, both rely on it.   The 67 is a Model 65 with a  Data
Address Translation unit (DAT box) - is supplied by a 8 x 32 bit TLB which
is in a cabinet that t'ed off the main CPU and is about the same size en
entire Vax 780 which would follow 10 years later.

Think about that for a minute -- an 8 word TLB.   At Intel we regularly
examine the different sizes of the different parts of the memory system.
Core 7 (aka Nehalem of a few years ago) has a two-level TLB: the first
level of TLB is shared between data and instructions. The level 1 data TLB
now stores 64 entries for small pages (4K) or 32 for large pages (2M/4M),
while the level 1 instruction TLB stores 128 entries for small pages (the
same as with Core 2) and seven for large pages. The second level is a
unified cache that can store up to 512 entries and operates only with small
pages.

Also it is also interesting to consider that while the AT&T folks came off
of Multics, a number of us university types that would work on earlier Unix
came from TSS and MTS (one 360/67).   In fact, TSS is still the only system
I ever used that lived in the debugger as your command system - which I
always thought was a cool idea.

As for what started this thread.   I think it is interesting that the long
term successful architectures in the market did have a excellent
compatibility stories. IBM with system 360 certainly set a high bar, and
DEC has nothing to be ashamed of, the different DEC lines, particularly the
Vax, did a great job here.    In truth, probably the best of pure
compatibility story has to be Intel.  The H/L registers of the 4004 are
still there ;-)   Seriously, the INTEL*64 is from an computer science
standpoint, not an architecture you would create from scratch.   But Intel
has completely understood the economics of SW compatibility.

Also, if you peeked inside a modern processor, you would discover they are
dataflow engines and put together with all of the modern computer science;
but there is about a 5% silicon tax paid for compatibility.  Clearly, my
siblings at Intel believe it's worth tax and the customers seem to keep
wanting it.

Clem

On Tue, Feb 16, 2016 at 8:15 AM, Dave Wade <dave.g4ugm at gmail.com> wrote:

> > -----Original Message-----
> > From: Simh [mailto:simh-bounces at trailing-edge.com] On Behalf Of Wilm
> > Boerhout
> > Sent: 16 February 2016 11:58
> > To: simh at trailing-edge.com
> > Subject: Re: [Simh] VAX/VMS
> >
> > Johnny Billquist schreef op 16-2-2016 om 12:49:
> > >
> > > No, it is not. Talk to IBM about S/360... :-) And there are some VAXen
>
> S/360 compatibility is only forward, and only to a certain point. S/360
> and S/370 are both 24-bit addressing and fairly compatible, but S/370
> (Mostly) has Virtual Memory as standard.
>
> Then came the "great divide" S/370XA. XA mode has 31-bit addressing and
> different I/O instructions. Some of the XA boxes will work is S/370 mode,
> but many won't.
>
> More recently IBM moved to 64-bit hardware. Again some will boot in 31-bit
> mode but more recent boxes need a 64-bit OS.
>
> So the earliest incarnations of "OS", which were I guess "MFT" which is
> basically a fixed number of partitions will run on later machines until you
> get to systems which will only run in 31bit mode. (XA Mode).
>
> OS/VS2 and its siblings MVS (This is the free version), MVS/SP (The paid
> for version) will only run on S/370 or later, not on 360, as they need
> Virtual Memory and it stops working at the same point as MFT when 31 bit
> only machines appear. There are also issues of Virtual Memory Page size
> which may stop MVS (the free version working) working on some hardware
> (there are patches to work round this).
>
> You also have issues over disk (DASD in IBM speak) support. So whilst MFT
> was written for a 1996 S/360 it would in theory run on an P390E from 1996
> so 30 years of computability. However, it would need older disks, which the
> P/390E cannot support.
>
> Of course these changes are really only to do with programs that run in
> supervisor state. User mode programs generally will run unchanged from 1966
> through to the present day, and the latest zOS a descendant of MVS will
> still run 24-bit applications.  I am pretty sure that until a few years
> many commercial sites, so mostly Cobol, still used the older "free"
> Fortran-66 compiler for the odd Fortran job.
>
> > > on which V7.3 will definitely not run. How about rtVAX for example.
> > >
> > I stand corrected. Please note that I had a marketing job once. It
> sticks...
>
> ... I also believe that some of the in-compatibility in IBM kit is to
> drive the hardware->software->Hardware->Software upgrade chain and keep the
> dollars rolling in...
>
> Dave G4UGM
>
>
>
>
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