[Info-vax] inertia or fundamentals about langages?

[Simon Clubley]

On 2019-05-26, Hans Vlems <jhlmvlems at gmail.com> wrote:
> Hoff,
> You wrote
> ?As for OpenVMS ports, I've seen three of those from the inside.  Two 
> more?RSX-11M to VAX/VMS, and this current x86-64 port?from the outside. 
>  Each had clever bits.  I found the Mach port to be the most clever. ?
>
> Could you elaborate on the last sentence please?
>

Back in the VAX/VMS days, there was an effort to port it to the
Mach microkernel. It seems to have been a proof-of-concept port
only and the work was never done to turn it into a production
quality version of VMS.

Pity it never turned into something. It would have certainly stopped
all the messing around with the 4 modes VMS needs when porting
VMS to a new architecture.

Outside of a microkernel, if you were to redesign VMS to be a two mode
architecture, then executive mode is the easiest to get rid of by
folding it into kernel mode (provided you don't mind a system crash
when executive mode code crashes :-)).

The most difficult extra mode to get rid of in the current VMS design
is supervisor mode. In the current design, you can't fold supervisor
mode into user mode without compromising the security of the system. 

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world