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:cl...@ccc.com]
*Sent:* 16 February 2016 13:58
*To:* Dave Wade <dave.g4...@gmail.com>
*Cc:* SIMH <simh@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.g4...@gmail.com
<mailto:dave.g4...@gmail.com>> wrote:
> -----Original Message-----
> From: Simh [mailto:simh-boun...@trailing-edge.com
<mailto:simh-boun...@trailing-edge.com>] On Behalf Of Wilm
> Boerhout
> Sent: 16 February 2016 11:58
> To: simh@trailing-edge.com <mailto:simh@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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