[Simh] Compatibility you can use Was: VAX/VMS

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On Sun, 21 Feb 2016 08:50:45 -0500
Clem Cole <clemc at ccc.com> wrote:

> To pick on DEC (or IBM), the later generations of their respective ISAs
> cannot boot the older OS – which Intel’s primary ISA can – and that is
> what started this discussion.

I can't speak to DEC's issues but with IBM has already been said, this was
by design. They were selling hardware. The OS and program products helped
them do that.

However, we see that Intel's hardware compatability is only of academic
interest because virtually none of the OS or apps for several generations
of Intel chips runs on any remotely current Intel-hosted OS. I already
pointed out many day-to-day incompatibilities between code running 32 bit
vs. 64 etc. on Intel today. You can blame Microsoft or Bell Labs or
even Richard Stallman but Intel has certainly been involved intimately with
much OS development on its platform and has continued to bork time after
time. 

We all know at the end of the day people buy hardware to run apps. We
also know most of the apps ever written for Intel are no longer useful even
if you could boot obsolete OS and run them. Any meaningful notion of
compatibility has to include the ability to continue to run your apps on
every new OS and hardware generation. With Intel you can't. You can point
all the fingers you want but that is the reality in the Intel environment.

In practice, several decades of software and development investment,
applications, and OS go up in smoke with each new generation of Intel
chips. In contrast IBM has preserved the customer's investments in
technology, development, and applications. IBM takes the loss on the OS
development but the customer's applications continue to run forever on the
latest platform. Intel is an ecosystem of churning, turmoil and waste.
That's something only an accountant could love.

As has been noted code from virtually the beginning of OS/360 still runs
today and furthermore can happily coexist with newly written apps without
any hoop jumping like relinking, recompiling, or needing multiple
libraries. It just continues to work. Software compatibility beats hardware
compatibility any day of the week. What's important is that your
application and development investment continues to be viable on each new
hardware platform with each new OS. That is what IBM has done, and it is a
combination of hardware and software designed to work together and boy does
it ever, as opposed to a pizza with everything on it spoiled by too many
chefs.

In terms of rubber meets the road upward compatibility what IBM has
delivered over the lifetime of OS/360->MVS-XA-ESA-z is infinitely more
valuable than compatibility on paper that nobody who runs Intel has ever
been able to take any practical advantage of.