Xref: utzoo comp.sys.amiga:34321 comp.sys.amiga.tech:5324
Path: utzoo!attcan!utgpu!utstat!jarvis.csri.toronto.edu!rutgers!iuvax!watmath!watcgl!jvkelley
From: jvkelley@watcgl.waterloo.edu (Jeff Kelley)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: AmigaOS is real-time?
Message-ID: <9881@watcgl.waterloo.edu>
Date: 24 May 89 18:05:28 GMT
References: <16100@louie.udel.EDU>
Reply-To: jvkelley@watcgl.waterloo.edu (Jeff Kelley)
Followup-To: comp.sys.amiga.tech
Organization: U. of Waterloo, Ontario
Lines: 35

In article <16100@louie.udel.EDU> MROBINSON@wash-vax.bbn.com writes:
>
>Is AmigaOS truly a real-time OS?

No.

>To me, real-time means that each system call is guaranteed to complete
>within a *defined* amount of time (which should be small).

The definition I use:

Real-time: The ability to respond to REAL-world events, such as interrupts,
	   in bounded TIME.

The AmigaOS, and in particular Exec, disables interrupts for arbitrarily
long periods of time.  For example, when a task loses the CPU because a
higher priority task becomes ready, interrupts are disabled while the lower
priority task is 'Enqueue'd on the task ready list, an operation for which,
in general, an upper bound on the time cannot be specified.

There are likely other areas, e.g. memory allocation, where similar
situations occur (though I've only looked at the code for context switches.)

The AmigaOS is not real-time, but it is typically responsive.  This is due
in part to the fact that it does not support virtual memory but primarily
because of well designed system hardware and a kernel designed to be
efficient and lightweight (just not real-time...)

I still love my Amiga, though.  Real-time is nice, but isn't essential
unless you're a missile tracking a jet fighter or a control circuit
in a nuclear reactor deciding whether or not to shut it down.

--
Jeff Kelley    National Research Council of Canada, Ottawa
   uunet!watmath!watcgl!jvkelley  	tel:   (613) 990-5924