[Info-vax] VMS internals design, was: Re: BASIC and AST routines

[Simon Clubley]

On 2021-11-26, Félim Doyle <felim.doyle at gmail.com> wrote:
> On Thursday, 25 November 2021 at 15:48:37 UTC, Dave Froble wrote:
>> VMS was designed and implemented for VAX, not generic computers.
>
> As I remember it, VAX/VMS was designed by DEC to be its best ever OS then the VAX hardware was designed and built to run it not the other way around. There were probably some mistakes made, unforeseen implementation issues and some miscommunications during parallel development of the hardware and software but the facilities that this combination provided, especially in comparison to the price range of other systems at the time, was revolutionary.
>

One of the biggest mistakes made is that DEC went to the trouble of
implementing a 4-mode architecture and then completely blew how it was
used.

That 4-mode architecture could have provided some really truly radical
internal security separation within VMS, but once you are in any of the
3 inner modes, you can get to any of the other inner modes so all those
extra modes were wasted from a security isolation point of view.

In case you are wondering, you can escalate from supervisor mode because
DCL has access to the privileges of the programs it runs even though it
doesn't actually need them. That kind of thing should have stayed within
the kernel so DCL never sees those privileges.

Just yet another VMS design "feature". :-)

Simon.

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