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From: kdarling@hobbes.ncsu.edu (Kevin Darling)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: How do we change the scheduler? (Was Re: Multitasking at home...)
Message-ID: <1991Jan30.131318.18064@ncsuvx.ncsu.edu>
Date: 30 Jan 91 13:13:18 GMT
References: <1991Jan18.231330.16290@Neon.Stanford.EDU> <7553@sugar.hackercorp.com>       <1991Jan21.004720.25985@ncsuvx.ncsu.edu> <12880@life.ai.mit.edu>       <1991Jan21.072642.23587@Neon.Stanford.EDU> <10620.tnews@templar.actrix.gen.nz>  <1991Jan22.215801.4557@Neon
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jbickers@templar.actrix.gen.nz (John Bickers) writes

>> For example, I believe the Amiga OS was derived from Tripos? by Metacomco?.
>> What was the original design decision behind the Amiga OS ancestors?
>
> AmigaDOS was apparently based on Tripos. This is the bit that does
> things like normal file management, loading programs, etc.
> There is another level to the OS that does the multitasking and
> inter-process stuff, called Exec. This is not related to Tripos.

I'm sure the CBM guys will let us know.  But in the meantime, I thought
y'all would be interested in part of a 1988 TRIPOS advertisement.
  <kdarling@catt.ncsu.edu>

---------------------------- begin quote -------------------------------

WHAT IS TRIPOS: The system was first developed some years ago in the
University of Cambridge in the U.K.  It was designed as a model of a
classical operating system.  In 1981 it was taken to the University of
Bath where work had been started on a 68000-based system.   TRIPOS
was ported to this hardware. Three years later, METACOMCO acquired the
rights and started a conversion which would be commercialized.

This work was assisted by the CBM-Amiga in March 1985 when they chose
the system as the kernel of their AmigaDOS.

DESIGN PHILOSOPHY: Maximum response speed was a major design objective
for TRIPOS. It is designed to have as few overheads as possible,
resulting in a fast OS for realtime applications.  Three areas where
this philosophy is clearly demonstrated are scheduling, memory management
and message passing.  The scheduler adopts a strict task-priority system.
There is no overhead for the time-slicing process required in a system
using "round-robin" type scheduling.  A task which is allocated processor
time continues to run until a higher priority task is ready to run or
until it suspends itself.

In the area of memory management, kernel primitives are provided for
allocating and freeing memory.  No checking is done to stop a program
using non-allocated space.  By adopting this non-memory-management
approach, all memory accesses can be executed as fast as the memory
allows, avoiding any clock cycles inserted by an MMU.  Clearly, the
applications software writer has to ensure that programs are well-behaved.

A similar philosophy is applied to the message-passing system.  All
communications within TRIPOS is done by sending and receiving packets.
These packets are areas of memory containing the information and are
passed by reference rather than copied.  Is is because of the memory
management philosophy that this method of message passing can be adopted,
avoiding the unnecessary duplication of memory.

KEY FEATURES:
  * True multitasking realtime OS
  * Small ROMMable code
  * Highly interactive and user friendly
  * Open architecture
  * Integrated debugger
  * Hierarchical filing system
  * RAM disk included
  * Device independent I/O
  * Support for windows

------------------------------ end quote -------------------------------