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From: geoff@desint.UUCP (Geoff Kuenning)
Newsgroups: net.unix
Subject: Re: Favorite operating systems query
Message-ID: <228@desint.UUCP>
Date: Thu, 19-Jun-86 06:28:10 EDT
Article-I.D.: desint.228
Posted: Thu Jun 19 06:28:10 1986
Date-Received: Sat, 21-Jun-86 10:29:05 EDT
References: <339@valid.UUCP> <452@geowhiz.UUCP> <2041@umcp-cs.UUCP>
Reply-To: geoff@desint.UUCP (Geoff Kuenning)
Distribution: net
Organization: SAH Consulting, Manhattan Beach, CA
Lines: 49

In article <2041@umcp-cs.UUCP> chris@umcp-cs.UUCP (Chris Torek) writes:

> >5) Real time support.
> 
> This is a valid criticism.  To do VMS real-time code, one writes
> a driver and installs it with system privileges; the driver then
> has direct access to the hardware---or rather, that is my understanding
> of the process.

Unfortunately for Unix, there is a lot more to doing a real-time
application than simply writing funny device drivers.  In fact, *lots*
of DEC customers do major real-time control (e.g., entire factories)
with DEC-standard hardware and drivers.  You can buy A/D, D/A, and
digital I/O interfaces from DEC, together with drivers and ISA standard
Fortran libraries.  Want to move a valve to a particular position?  Call
ADOUT with the appropriate parameters.  And so forth.

Furthermore, VMS has a plethora of system services that are absolutely
necessary for general-purpose real-time applications.  For example,
there are many ways to handle asynchronous I/O and interprocess
synchronization/communication (at least System V finally caught up with
this last one).  Again, these are readily available via ISA-standard
libraries.

Finally, VMS has numerous scheduler features (e.g., fixable priorities,
notification of I/O completion) that are useful to real-time programmers.
None of these are in Unix, and most are fairly difficult to add.

This is not to imply I'm a VMS fan.  I detest VMS as a user's and as
a programmer's system.  But it *does* have facilities that are just
plain missing from Unix, and a lot of them are necessary for real-time
applications.

Finally, somebody else made the statement that DEC and Masscomp are the
only manufacturers who have real-time operating systems.  Nothing could
be further from the truth.  In the micro world, you have MTOS, VRTX,
iRMX, something from Motorola (I forget the name), Charles River's UNOS,
Wicat's MCS (at least it's advertised as real-time), the Masscomp
offering, and several others.  In minis essentially everybody has a
real-time offering:  DEC, DG, Prime, Tandem, HP (they now claim to
have a real-time Unix).  There are even real-time systems for mainframes
(SABRE, the airline-reservations system, jumps to mind;  the military
does real-time on Crays).  There are many, many more that I have left
off the list simply because I'm doing it off the top of my head.  But
I think I've made my point.
-- 

	Geoff Kuenning
	{hplabs,ihnp4}!trwrb!desint!geoff