[Simh] Is Alpha AXP in SIMH's future?

[lists at openmailbox.org]

On Tue, 3 Mar 2015 23:27:28 -0800
Mark Pizzolato - Info Comm <Mark at infocomm.com> wrote:

> On Tuesday, March 3, 2015 at 11:16 PM, lists at openmailbox.org wrote:
> > On Tue, 3 Mar 2015 13:34:51 -0800
> > Sergey Oboguev <oboguev at yahoo.com> wrote:
> > 
> > > My comment was is not about Intel vs. non-Intel, but about having
> > > 64-bit as a native type in host machine instructions and leveraged by
> > > the compiler, rather than simulated by 32-bit host operations.
> > 
> > I thought there was no direct way to do math on 64 bit integers in 32
> > bit Intel and simulation by 32 bit host operations (add, adc) would be
> > required, as opposed to other platforms which (I believe) have
> > instructions for 64 bit integer math even in 32 bit mode (i.e. SPARC).
> 
> That is exactly Sergey's point.  Running a 64bit simulator on a 32bit
> Intel platform (even with a compiler which has 64bit types) will be
> significantly slower than running a simulator compiled for a 64bit host.

I understood that it applied to Intel. I just didn't remember it also
applies to some (most?) other 32 bit platforms.

Even so, there is a big difference between being "significantly slower" and
"not supported at all" and that was the point of my question/discussion.
Today Alpha emulation is not supported at all on 32 bit Linux AFAIK.

QEMU is horribly slow but it is still valuable because it supports a lot of
machines pretty well. Hmm, now that I think of it I need to check if
qemu-alpha will run OpenVMS Alpha. If anybody knows one way or the other
and it's not too far off-topic please update us.

Anyway, if SIMH could support an Alpha machine capable of running OpenVMS
and would build and run on 32 bit Linux and everywhere else it builds today
I don't think anyone would complain about the performance. Either you run
it on a 64 bit host and get the best performance you can given the software
or you run it on a 32 bit host for whatever reason and accept that it runs
slower than it would on a 64 bit host. But that is much better than having
no choice at all for 32 bit Linux which is where we are now unless
qemu-alpha is there already.