Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!killer!elg
From: elg@killer.Dallas.TX.US (Eric Green)
Newsgroups: comp.sys.amiga
Subject: Re: OS/2 vs AmigaDOS
Message-ID: <7988@killer.Dallas.TX.US>
Date: 3 May 89 02:51:43 GMT
References: <16952@usc.edu>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 39

in article <16952@usc.edu>, papa@pollux.usc.edu (Marco Papa) says:
> In article <6730@cbmvax.UUCP> daveh@cbmvax.UUCP (Dave Haynie) writes:
>>Shared libraries and virtual memory are more
>>sophisticated approaches to the problem.  OS/2 and UNIX have virtual memory;
> 						              ^^^^^^^^^^^^^^
>>I predict Amiga's with MMU's will have it before the end of the year.
> Do you mean 1.4 will support virtual memory and will show up by year's end?
> This would be just great! This is the FIRST time I've heard anything like this
> mentioned (not evn on BIX closed conf. I heard it). No more GURUs if you have
> an A2620 or A2630.

Sorry Marco. Virtual memory is no problem. Process protection
(GURU-busting) is. AmigaDOS assumes one big huge shared memory address
space with multiple cooperating programs occupying it. Process
protection thus must be on a per-block basis, which the MMU on the
2620 will NOT do if I recall my Motorola MMUs correctly. Virtual
memory, on the other hand, is a piece of cake by comparison. Just map
in the CHIP and ROMs, map in your page faulter (which runs the hard
disk handler in "real" mode), and presto -- instant multi-megabyte
FAST.  Or not so presto... there's some problems involved in getting
your pages to and fro from the hard drive. But you get the picture.
There's no major OS rewrite or major hardware modification involved,
just a bit of (admittedly tricky) software to control the hardware
already there, in a way totally transparent to applications programs
(when they request FAST, they have no idea if it's "really" memory, or
not). 

So if your idea of heaven is to have a 10 megabyte RAD: device, and
keep Excellence, X-WIndows, Superbase, and a half dozen other programs
all running at the same time with no fear of running out of memory,
you'll love what's coming. On the other hand, if your idea of virtual
memory includes process protection, you're just plain out of luck.


--
|    // Eric Lee Green              P.O. Box 92191, Lafayette, LA 70509     |
|   //  ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg     (318)989-9849     |
|  //    Join the Church of HAL, in worship of all computers  with          |
|\X/   three-character names (e.g. IBM and DEC). White lab coats optional.  |