From: "Alexei A. Frounze" <see_below AT the_messasge_body DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: far pointers
Date: Mon, 12 Jun 2000 20:10:21 +0400
Organization: None
Lines: 29
Message-ID: <39450B6D.B6BFADA1@the_messasge_body.com>
References: <Pine DOT SUN DOT 3 DOT 91 DOT 1000611090320 DOT 22597K AT is> <39437974 DOT A97A4769 AT the_messasge_body DOT com> <3944d5d1$0$81198 AT SSP1NO17 DOT highway DOT telekom DOT at>
NNTP-Posting-Host: ppp101-53.dialup.mtu-net.ru
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
X-Trace: gavrilo.mtu.ru 960827027 21469 212.188.101.53 (12 Jun 2000 16:23:47 GMT)
X-Complaints-To: usenet-abuse AT mtu DOT ru
NNTP-Posting-Date: 12 Jun 2000 16:23:47 GMT
X-Mailer: Mozilla 4.72 [en] (Win95; I)
X-Accept-Language: en,ru
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

Florian X wrote:
> 
> >V86 has all the features of PMode. Just addressing inside the linear space
> >is the same as in real mode. This is the basic difference.
> 
> But why do we need real mode, why is there an real mode?

1. Because of beackward compatibility
2. Because V86 could not live alone. If BIOS started up in V86, someone had
to provide V86 monitor functions which is in fact usually a part of an OS.
By default BIOS have nothing about any OS. And by the way, if BIOS booted
MBR while CPU is in V86 or PMode, an OS would have some troubles going to
the most privilege level - ring #0.

If you wanna know more about PMode, just download some docs about systems
programming from Intel:
1. INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986 [plane text - 200KB
zipped] (available at my site)
2. Intel Architecture Software Developer’s Manual Volume 3: System
Programming [PDF - 3MB zipped] (available at http://developer.intel.com)

Bye.
Alexei A. Frounze
-----------------------------------------
E-mail:   alexfru [AT] chat [DOT] ru
Homepage: http://alexfru.chat.ru
Mirror:   http://members.xoom.com/alexfru