From: Brendan Simon <brendan AT rdt DOT monash DOT edu DOT au>
Date: Fri, 2 Feb 1996 16:56:19 +1100
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Protected Mode Questions


I wish to know how often one can expect a djgpp program to be in protected
mode and how often in real mode ???

I know djgpp only produces PM code.  I'll rephrase the question.
When a PM program is running, what percentage of the time is the CPU in PM,
and what percentage in RM.

What are the main reasons for the CPU switching to RM.

Is it system call stuff ??  Such as file system access, timer ints, bios,etc ???

If so, is it possible to write device drivers or other OS type routines to
keep the CPU in PM as much as possible ??
Am I asking the impossible, or not worth trying since I really want a simple
protected mode OS ???


I ask this because I am under the impression that mode swaps are expensive
in terms of performance, and if I/we can eliminate the swaps as much as possible
then we will be much better off.


What I really want is a MS-DOS compatible OS that runs completely in PM.
Is this possible, or am I talking OS-2, or Linux.

Any thoughts,

Brendan Simon
brendan AT rdt DOT monash DOT edu DOT au


PS. I've seen a MS-DOS compatible kernel called FREE-DOS.  I like the concept
behind it as it's free, is a complete kernel with source and means I can
completely run free of any MS software on my machine.  MS policies to software
do not sit well with me.