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From: jxf@orion.cis.ksu.edu (Jerry Frain)
Newsgroups: comp.sys.mac.system
Subject: Re: True Multitasking, True Object-oriented, True anything.
Message-ID: <1991Jan22.082018.14641@maverick.ksu.ksu.edu>
Date: 22 Jan 91 08:20:18 GMT
References: <6082@stpstn.UUCP> <1991Jan22.035748.275@d.cs.okstate.edu>
Sender: news@maverick.ksu.ksu.edu (The News Guru)
Reply-To: jxf@orion.cis.ksu.edu (Jerry Frain)
Organization: Kansas State University, Department of Computing and Information Sciences
Lines: 73

In article <1991Jan22.035748.275@d.cs.okstate.edu> minich@d.cs.okstate.edu (Robert Minich) writes:

>How about if we just use "preemptive multitasking" to
>describe itself and let "multitasking" refer to any number of schemes where
>two or more otherwise unrelated threads of execution are active at one
>time?  We can use "multithreaded application" to describe a single
>program that has multiple threads of execution.

I would agree with this argument, except for one thing.  The term
"multitasking," I believe, is derived from the feature of Ada to
allow the programmer to establish separate threads of control.

The Ada term for a thread is a "task."  Thus, I believe, the term
multitasking was coined from the multiple-tasking feature of Ada.
This use of "multitasking" is synonymous to Mr. Minich's definition
of "multithreading" (as it should be).

>Here are the definitions
>I propose:

>	multiprogramming        -- multiple tasks executing with one
>	                           thread per task (typical time sharing)

Correct.

"Multiprogramming"is defined as a system which has the ability to have
more than one program (job) in main storage, and have the processor
switch rapidly between the programs so that they appear to be executing
concurrently.

"Time-sharing" is multiprogramming except that now interactive services
are provided to users who have on-line terminals while larger jobs
execute in the background.

I defined "multitasking" (informally) above, so I won't repeat myself.

"Preemptive multitasking" does not _really_ make sense.  "Preemptive"
certainly does not describe "multitasking."

We already know that the Mac is time-sharing.  To say that it is also
multitasking adds a new dimension which is not accurate, especially if
you believe the part about the origin of the term "multitasking" stems
from the Ada language.

The words "preemptive" and "cooperative" describe the way in which jobs
in a multiprogramming/time-sharing environment relinquish the processor
so that another job may be scheduled for execution.

In this context, "preemptive" and "cooperative" describe one characteristic
of the scheduling policy used by the operating system.

That is, a "preemptive scheduler" typically suspends a job (process) after
a "time quantum" has expired, and a "cooperative" scheduler waits until the
currently-running job relinquishes the processor *on its own*.

Thus, the Macintosh implements a cooperative _scheduler_.  Unix, AmigaOS,
et. al. perform preemptive _scheduling_.

>	True <anything> (tm)    -- a term used by those who don't know
>	                           how to communicate

Depending upon its use, of course.  In this case, I would tend to agree.

Regards,

  --Jerry

--
Jerry Frain -- Systems Programmer               Kansas State University
                                        Department of Computing & Info Sciences
Internet : jxf@cis.ksu.edu                         Manhattan, Kansas
UUCP     : ...!rutgers!ksuvax1!jxf