[Info-vax] VAX VMS going forward

[Arne Vajhøj]

On 7/29/2020 11:43 AM, Stephen Hoffman wrote:
> On 2020-07-29 15:07:02 +0000, Arne Vajhj said:
> 
>> On 7/29/2020 10:50 AM, Stephen Hoffman wrote:
>>>
>>> 4) Allow 32-bit apps to run in parallel and in separate processes, 
>>> with developer and 64-bit API work toward 64-bit apps pending 
>>> retirement of the 32-bit APIs and apps, and allowing a transition to 
>>> 64-bit apps to happen over a decade or more, and which makes this 
>>> 64-bit app transition more incremental and thus somewhat less 
>>> disruptive.
>>
>> If there is no 32 and 64 bit mode in the CPU then there is no concept 
>> of 32 bit and 64 bit apps.
> 
> Alas, there is exactly such a concept.
> 
> OpenVMS has it, too.
> 
> You're seemingly focused solely on the processor itself, and not in the 
> operating system.

That is the common definition of segmented memory how the CPU get fed 
addresses.

> The operating system presents an abstraction of the hardware, including 
> an abstraction of the processor.

Not in general.

If that was the case then program would run on any CPU as long as
the OS match. And as we all know that is not the case.

> In this case, OpenVMS presents segmented addressing.

Not really.

VMS has memory split in some regions. And some regions are
dedicated to certain purposes. I believe that is very
common among OS'es.

And VMS has a relative unique (NonStop supposedly do the same) feature
where it has two pointer sizes.

And the 32 bit pointers can obviously not address all memory.

Two different pointer sizes and some pointers not being able to address
all memory is messy.

But it is not segmented memory.

And it does mean that there is 32 and 64 bit apps.

Arne