Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!uwvax!oddjob!gargoyle!ihnp4!homxb!mtuxo!mtune!codas!killer!usl!usl-pc!jpdres10
From: jpdres10@usl-pc.UUCP (Green Eric Lee)
Newsgroups: comp.sys.amiga
Subject: Re: The Next Generation
Message-ID: <360@usl-pc.UUCP>
Date: Tue, 17-Nov-87 13:25:48 EST
Article-I.D.: usl-pc.360
Posted: Tue Nov 17 13:25:48 1987
Date-Received: Sat, 21-Nov-87 13:36:12 EST
References: <2785@megaron.arizona.edu> <17218@glacier.STANFORD.EDU>
Organization: Univ. of Southwestern La., Lafayette
Lines: 39

In message <17218@glacier.STANFORD.EDU>, jbn@glacier.STANFORD.EDU (John B. Nagle) says:
>    1.  Given the way that RAM prices are declining while
>	disk access times are not improving, virtual memory
>	looks like an idea whose time has passed.  

Only if you have a single-tasking operating system. Certainly you can
get enough physical memory nowadays to run ANY respectable program.
But what if you have FIFTEEN 2 megabyte programs loaded up? Sure, they
probably aren't all going to run at once... the other 14 are most
probably just going to be sitting there, hung waiting for input,
inactive. But virtual memory, in this case, is just providing the
book-keeping so that you don't have to manually shuttle those other 14
programs in and out of memory (i.e. via exiting each one of them and
losing your place in whatever you were doing in them -- in other
words, exactly what multitasking was supposed to eliminate).

>    3.  Memory protection is desirable, but a true protected operating
>	system would require that the operating system keep track of
>	all the resources requested by a user program and be able
>	to take them back when a program exited abnormally.  Tripos
>	(alias AmigaDos) does not do the bookeeping to allow this.

We hashed over this eons ago on the net. Most of us agree that, with
fairly minor alterations to the memory manager and i/o libraries, it
CAN be done with TRIPOS. The problem is that without a memory
management unit, it would be VERY expensive.

A memory management unit would allow this book-keeping to be handled
much more transparently than it currently could be....

One very good scheme for AmigaDOS/TRIPOS would be to have half the
virtual memory globally mapped, i.e. so that all the processes could
pass messages to each other, and the other half locally mapped, for
your actual program and its data. 

--
Eric Green  elg@usl.CSNET       from BEYOND nowhere:
{ihnp4,cbosgd}!killer!elg,      P.O. Box 92191, Lafayette, LA 70509
{ut-sally,killer}!usl!elg     "there's someone in my head, but it's not me..."