[Info-vax] New CEO of VMS Software

[Arne Vajhøj]

On 1/6/2024 7:27 PM, Dan Cross wrote:
> In article <unck70$p3mp$4 at dont-email.me>,
> Lawrence D'Oliveiro  <ldo at nz.invalid> wrote:
>> On Sat, 6 Jan 2024 15:59:58 -0500, Arne Vajhøj wrote:
>>> VMS has only 64 bit code but both 32 bit pointers and 64 bit pointers
>>> (32 bit pointers getting extended to 64 bit addresses).
>>
>> Not sure how you can have 64-bit code without 64-bit addressing ...
> 
> Of course you're not.  "64-bit code" for something like x86
> refers to details of the processor mode and e.g. the handling
> of the REX prefix.  On Alpha or Itanium, presumably that means
> using the 64-bit ISA that uses e.g. 64-bit registers and so on.
> 
> But in either case, that's distinct from data pointers in
> userspace are truncated represented as 32-bit values, as only
> the low 2GiB of the address space is used by VMS applications.

A VMS application with all pointers being 32 bit only
use the low 2 GB.

A VMS application with all 64 bit pointers or a mix of
32 bit and 64 bit pointers can use more (in theory 4 EB,
but I believe both HW and VMS has limits lower than that).

Arne