why unix is not a real-time system

why unix is not a real-time system

Post by Lawson Hans » Tue, 18 Nov 1997 04:00:00




>Why unix is said to be not a real-time system?

A "real-time" system is one where you can guarantee that
you will get a response within a pre-defined time frame.
There are some Unix systems (e.g.: MERT (?), and QNX)
which ARE "real-time", but most other Unix systems are
configured/designed to be more equitable multi-user systems
where every user usually gets a relatively fair share of
the computer resources and in that form it is virtually
impossible to guarantee any particular short time frame
(i.e.: millisecond, or microsecond) response.

Quote:>I'd appreciate your replies.
>With thanks
>Iram

I hope that helps (without going in to any real detail).

Best regards,

Lawson Hanson

 
 
 

why unix is not a real-time system

Post by J. Kan » Wed, 19 Nov 1997 04:00:00


|>  Why unix is said to be not a real-time system?

Which Unix?  Most implementations I'm familiar with do not have a
deterministic scheduler, which is a must for real-time.

--

GABI Software, 22 rue Jacques-Lemercier, 78000 Versailles, France
        I'm looking for a job -- Je recherche du travail

 
 
 

why unix is not a real-time system

Post by Mark Ha » Thu, 20 Nov 1997 04:00:00


: where every user usually gets a relatively fair share of
: the computer resources and in that form it is virtually
: impossible to guarantee any particular short time frame
: (i.e.: millisecond, or microsecond) response.

the "fair share" part hasn't been true for a long time: most Unixen
provide some form of higher-than-normal-processes priority,
often with run-till-they-yeild classes.  HPUX does, for instance,
as does Linux.  Linux actually provides a pretty wide variety
of support, from hard to soft, including "firm" ;)

 
 
 

1. why unix is not a real-time system

Because the process scheduler on standard UNIX systems doesn't
guarantee that any particular process will run within a given amount
of time.  There ARE real-time versions of unix, but they have a
non-standard kernel--in particular the process scheduler must be
completely rewritten.

Aaron
Unix Systems Admin

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