[Simh] VAX/VMS

Tue Feb 16 11:00:03 EST 2016

On 2016-02-16 16:16, Dave Wade wrote:

> I think it is also interesting to compare the Intel architecture which
> was designed to be economical with Silicon against the M6800, M6809 and
> the M68000 which were designed to be programmer friendly, and of course
> note the similarities between the 68000 & S/360 with 16 general purpose
> registers and orthogonal instruction set) and wonder where we would be
> today had IBM chosen them for its PC rather than the 8086 which I assume
> was cheaper…

I might be out on a limb here, but I think one reason that IBM went with 
the 8086 was that Intel could in fact deliver. Motorola had more issues 
with actually delivering large quantities, in time.

Also, the M68000 would be more similar to a PDP-11 or a VAX, I would 
think, except the fact that the 68000 wasn't as properly orthogonal. It 
actually have a lot of warts if you start looking closely.

	Johnny

>
> Dave
>
> G4UGM
>
> *From:*Clem Cole [mailto:clemc at ccc.com]
> *Sent:* 16 February 2016 13:58
> *To:* Dave Wade <dave.g4ugm at gmail.com>
> *Cc:* SIMH <simh at trailing-edge.com>
> *Subject:* Re: [Simh] VAX/VMS
>
> 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
> <mailto:dave.g4ugm at gmail.com>> wrote:
>
>      > -----Original Message-----
>      > From: Simh [mailto:simh-bounces at trailing-edge.com
>     <mailto:simh-bounces at trailing-edge.com>] On Behalf Of Wilm
>      > Boerhout
>      > Sent: 16 February 2016 11:58
>      > To: simh at trailing-edge.com <mailto: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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