Path: utzoo!mnetor!uunet!husc6!bloom-beacon!mit-eddie!ll-xn!ames!oliveb!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.atari.st
Subject: Re: About Atari's, Mac's, and IBM's
Message-ID: <51972@sun.uucp>
Date: 4 May 88 17:47:03 GMT
References: <5419@ucbvax.Berkeley.EDU> <226500010@trsvax> <213@bdt.UUCP> <4738@cup.portal.com>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 30

In article <4738@cup.portal.com> Thomas_E_Zerucha@cup.portal.com writes:
>The 386 has a 'virtual real memory mode' (no, that is not a contradiction,
>it emulates an 8086 address space in paged memory, so you can still play
>segment overlap games (theoretically)), and there may be one or more products
>out that take advantage of this, but I don't know how "protected" it would
>be.

The Virtual 8086 Mode of the '386 allows programs to run as though they 
were running native on an 8086. The 1 meg address space of the 8086 can
be mapped thru the '386 MMU to any space in memory (and paged in and out)
and the I/O calls are trapped so that the supervising OS (a so called 
Hypervisor) can take the appropriate action. Entire sections of memory
such as the video display ram area, can be protected to cause traps so
that writing directly to the bits can be emulated. Strangely enough because
it takes longer to emulate video after the trap than it does to emulate
the BIOS call, programs that *don't* write directly to the video ram
run faster than those that do. (Sort of poetic justice I guess). Sun uses
this mode on the Sun 386i workstation to run DOS programs under UNIX.

On a completely different note, at the Amiga developers conference Commodore
showed a Transputer board that could be plugged into the 2000. This was only
a 'technology' demonstration and I don't think they could make it into a 
product in less than a 18 months maybe longer. They also gave out copies of
the 1.3 OS in ROM so that developers could upgrade their machines. All in
all and interesting time..


--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.