Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!ukma!nrl-cmf!ames!killer!linimon
From: linimon@killer.UUCP (Mark Linimon)
Newsgroups: comp.os.misc
Subject: Re: timeliness of real-time [was: Re: Realtime OS's]
Summary: parameters of real-time
Keywords: Realtime
Message-ID: <4702@killer.UUCP>
Date: 5 Jul 88 19:22:30 GMT
References: <10450@udenva.cair.du.edu> <8411@pur-ee.UUCP> <797@taux01.UUCP> 
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 33

In article , webber@aramis.rutgers.edu (Bob Webber) writes:
> Of course, my own interests are in...
> being able to guarentee that certain things will get done in a given
> 60th of a second time slice.  Is this the same neighborhood the ``real''
> realtime people are interested in, or do they want finer grain control?
> 
> --- BOB (webber@athos.rutgers.edu ; rutgers!athos.rutgers.edu!webber)
> 

To some extent, the phrase "real-time" has become marketingspeak.
Several classes of applications exist.  Heavy image processing applications
may require response down in the 1 to 10 microsecond range.  (Obviously
beyond a certain point you have to build dedicated hardware, sometimes
in conjunction with a slower microprocessor.  This is fairly common).

Machine control applications oftentimes are satisfied by response times
in the low milliseconds.  Most anything moving a stepper motor or
engaging a solenoid will be in this category.

As far as I can tell the common denominator that various people use the
"real" in "real-time" to mean, is that the response is *guaranteed* to
happen within this time.  In this sense an (untweaked) Unix kernel
is not real-time, due to its statistical behavior.  (Several manufacturers
have done such tweaking, by the way).

I am currently trying to gather together my notes and lists of
various real-time products on the market.  Further input solicited
by email, I will try to summarize to this newsgroup within two
weeks, maybe by the end of this week.

Mark Linimon
Mizar Digital Systems
sun!convex!mizarvme!linimon