[Dailydave] luckily, there are no dumb questions

[Bruce Ediger]

On Thu, 7 Jun 2007 dan at geer.org wrote:

> How is it so that MS Windows uses only Rings 0 & 3?
> An engineering answer, a marketing answer, and/or
> an historical answer would be welcome.  Don't know
> why I never thought to ask before, but I'm asking
> now.  (And if I'm really wrong, please tell me what
> uses 1|2.)

Here's some (now quite amusing!) material from 1998:
http://www.windowsitlibrary.com/Content/435/01/1.html

"To effectively support both RISC and Intel CPUs, Windows NT uses only two
  rings in its design, Rings 0 and 3."

I don't know how much credence to lend to early material about NT.  It's pretty
obvious that marketing drove most of the "technical" stuff available. For
example, obvious NT predecessors like Unix and Mach and VMS hardly got a
mention in the 1st Edition of "Inside Windows NT".

This collection of papers from the "DEC Technical Journal":
http://www.hpl.hp.com/hpjournal/dtj/vol4num4/toc.htm
doesn't seem to mention "rings" at all, which seems strange.
The "RISC" CPU mentioned in the 1998 material is the Alpha.
DEC clearly wanted VMS to run on Alpha CPUs, and VMS needed
4 rings.  Looks like maybe DEC used "PALcode" to do rings
for OpenVMS on Alphas.