[Info-vax] VAX VMS going forward

[Arne Vajhøj]

On 7/24/2020 1:54 PM, Simon Clubley wrote:
> On 2020-07-24, johnwallace4 at yahoo.co.uk <johnwallace4 at yahoo.co.uk> wrote:
>> Obviously UNIX isn't VMS.
> 
> No it isn't. And one other difference is that every program run
> in a Unix environment gets it's own private process which is then
> terminated when the program exits. It doesn't really matter if
> the program is running in 32-bit mode or 64-bit mode as far as
> the shell is concerned.
> 
> However, in VMS, DCL shares the same process as the programs
> it runs and P1 space is currently right in the middle of where
> the flat 64-bit address space would be for user programs.
> 
> So, how do you handle running both flat 32-bit programs and
> flat 64-bit programs within the same process space as DCL ?
> 
> Do you declare that you are only running either flat 32-bit or
> flat 64-bit programs exclusively when you login or is the
> flat 32-bit or flat 64-bit image type exclusively some kind of
> an image attribute and you can run both during the same DCL session ?
> 
> In that case, how do you keep P1 space at its current location
> for flat 32-bit applications but then move it out of the way when
> you want to run a flat 64-bit application ?
> 
> These are the types of issues you don't have to deal with in Unix
> because of the Unix design.

I am a bit confused.

VMS does not have 32 and 64 bit mode.

There is hundreds or thousands of VMS API's and
compiler generated code that use 32 bit
compressed addresses.

But changing all that to use full 64 bit addresses
does not really matter for DCL.

And P1 addresses are not really a problem. Just let
the new images starting using addresses at 4GB.

Arne