[Info-vax] VAX VMS going forward

[Simon Clubley]

On 2020-07-23, Stephen Hoffman <seaohveh at hoffmanlabs.invalid> wrote:
> On 2020-07-22 16:40:48 +0000, Robert A. Brooks said:
>
>> Paul Anderson and I have largely scrubbed any VAX-specific stuff from 
>> the build command procedures and MMS description files, and in some 
>> cases from the source, in order to make things more readable.
>
> Ditching 32-bit source code and 32-bit conditionals can make the source 
> code much simpler, particularly when the source code is working with 
> 64-bit values.
>
> Lots of limitations in the older 32-bit APIs, too. Particularly as the 
> same source code starts to adopt 64-bit operations and addressing.
>
> Going to flat 64-bit addressing would simplify this further, though a 
> decade-long migration to flat 64-bit addressing would be exceptionally 
> fast.
>

If flat 64-bit addressing is ever going to happen, it's going to have
to come with some kind of a 32-bit addressing mode for existing code.

There's just too much going on at an unabstracted low level in VMS
code for flat 64-bit addressing to be viable by itself without any
other addressing modes.

You would also need some way of supporting the current 32-bit/64-bit
mixed addressing unless you outright discontinue such support.

P1 space would also be right in the way of a flat 64-bit addressing
mode so all the code which uses P1 space would have to be rewritten to
support flat 64-bit addresses because P1 space would have to be moved
well out of the way.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.