[Info-vax] HP Users Hope Whitman Can Persuade Oracle to Change Itanium Decision

[John Wallace]

On Oct 1, 2:37 am, Arne Vajhøj <a... at vajhoej.dk> wrote:
> On 9/28/2011 5:17 PM, Richard B. Gilbert wrote:
>
> > If it were possible to port VMS to the X86 platform, I think somebody
> > would have done it long ago! Both VMS-VAX and VMS-Alpha have hardware
> > dependencies that the X86 platforms cannot satisfy easily, or at all!
>
> I think that is a myth.
>
> If there was a will (to fund the effort) to do it, then it
> could be done.
>
> VMS has already been through 2 arch migrations.
>
> If something is missing in x86-64 then the OS would need
> to change to fill the gap.
>
> Arne

"If something is missing in x86-64 then the OS would need to change to
fill the gap."

There is at least one other possibility to look at. x86-64 changes to
fill the gap.

Reasonably widely understood is the fact that today's x86-64 chips and
systems don't actually yet address the high end IA64 market - the
ultra-massive-memory, ultra-massive-SMP systems that presumably some
customers are paying good money for. Proliant still "only" goes up to
64 cores and 2TB of memory. Presumably that's not enough for some
people's apps in a quasi-general-purpose computer (ie not a specialist
supercomputer of some flavour).

But I suspect if we wait a bit, x86-64 continues to grow upwards,
needing no significant/specific funding from HP. Whereas IA64 only has
one customer, and they have to fully fund everything.

On the other hand it is now clearer to me that there is a genuine
issue with the number of registers needed to support "legacy" (="stuff
that works") VMS code on x86. x86-64 has quite a few general
registers, but many modern processors have more. In both cases, there
are probably more registers implemented than are visible to the
programmer; many of them are hidden by "register renaming" and such
and are there to support things like speculative execution and the
like. I wonder what it would take to make enough of them visible again
(vs the costs of code changes in VMS to support a 16-register world).
Making the registers visible is probably a silly idea, given that it
would likely need changes to instruction encodings etc, so let's
forget that.

So the medium term choices look like: HP (ie HP customers) pay to stay
with IA64 or HP pay to port the VMS code.

Any thoughts from anyone on posting (some or all of) the bootcamp
materials?