Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!spool.mu.edu!uunet!bu.edu!polygen!jerry
From: jerry@polygen.uucp (Jerry Shekhel)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: NeXT/Amiga Flamage: Get a life.
Message-ID: <1062@grant.UUCP>
Date: 28 Apr 91 15:46:34 GMT
Article-I.D.: grant.1062
References: <6hdG18ik1@cs.psu.edu> <1748@sjfc.UUCP> <20875@cbmvax.commodore.com> <1991Apr23.201029.9844@wpi.WPI.EDU> <12764@aggie.ucdavis.edu>
Reply-To: jerry@grant.UUCP (Jerry Shekhel)
Organization: Polygen Corporation, Waltham, MA
Lines: 26

In article <12764@aggie.ucdavis.edu> s110a010@deneb.ucdavis.edu () writes:
>
>Now put the 80486 in protected mode and it's REALLY
>nice, but unfortunately DOS still operates in real mode.  So does it all
>make sense?
>

Well, DOS also runs in Virtual 86 mode.  This is a special case of protected
mode in which the running program is fooled to think it's running in real
mode, while the OS can do all sorts of tricky memory mapping and paging/multi-
tasking underneath.  There are several (7?) special debug registers which
allow the OS to trap on any kind of access to any memory location or range of
memory locations.  This is how Windows is able to put DOS processes into
windows on the screen -- it traps on direct writes to the video buffer and
redirects the output into a window.  I think the whole design of the [34]86
is technically ingenious, although I do agree that the instruction set could
be better.  "What?!  The name of the program counter is ECS:EIP?!"
--
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| JERRY J. SHEKHEL  | POLYGEN CORPORATION  | When I was young, I had to walk |
| Drummers do it... | Waltham, MA USA      | to school and back every day -- |
|    ... In rhythm! | (617) 890-2175       | 20 miles, uphill both ways.     |
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|           ...! [ princeton mit-eddie bu sunne ] !polygen!jerry             |
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