Message-ID:	<B0000044976@datasoft.datasoft.com.br>
From:	"Cristovao Braga" <cbraga AT datasoft DOT com DOT br>
To:	"djgpp list" <djgpp AT delorie DOT com>
Subject:	Re: Ring 0?
Date:	Wed, 5 Mar 1997 11:35:51 -0300
MIME-Version:	1.0

Programs in protected mode run in any of four rings, being 3 (or 0, I don't
know for sure) the most privileged one and 0 (or 3) the least. Programs in
ring 3 can access all the memory of those running in the lowest rings,
those in ring two can access rings 0, 1 and 2 but not 3, etc.

That's widely used in Windows NiceTry and OS/2 to make the system stable.
In Windows NiceTry 4.0, the kernel and some parts of the file system run in
ring 3 (correct me if I'm wrong) and all the rest in ring 0. It makes it
completely impossible for an ordinary program to corrupt kernel data.

In NT 3.x, the video and file subsystems also were in ring 3, but MS moved
them to ring 0 to achieve speed gains, since ring switches eat a lot of cpu
time. In Win95, everything runs on ring 0.

Cristovao Braga.
cbraga AT datasoft DOT com DOT br

> From: Paul Derbyshire <ao950 AT FreeNet DOT Carleton DOT CA>
> 
> What exactly is "ring 0"? A page on optimizing code using CWSDPR0
> mentioned it. But it's not clear to me what it is. I assume it isn't a
> modem thing...:)

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