Re: ADA os talk

[Kilgallen@SpamCop.net (Larry Kilgallen)]

In article <9mgg0p$26j$1@nh.pace.co.uk>, "Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org> writes:

> Like I said, my memory of the situation whas that techniques were possible
> under VMS to run realtime, but that VMS wasn't designed to specifically
> provide some kind of realtime mode. Sort of a case where if you had enough
> privileges and enough priority and could keep anything else from taking
> precidence, you could convince yourself that you had fixed latency and
> weren't going to get swapped out. This is different than having a process
> that the OS manages in realtime mode and guarantees you that none of this is
> going to fail.

Absolutely VMS is designed so that you need privilege to alter its
behavior.  By default there is fair treatment for all, and that is
certainly inadequate for realtime needs.  The controls to tweak,
however, are all documented as being "for realtime", and those of
us who pass them every day (and ignore them) tend to presume the
priority mechanisms are adequate.  The scheduling algorithm has
a different behavior in the upper half of the priority range,
for instance, specifically for realtime.