PM> Most cpu architectures don't have more than two levels - kernel
PM> and user.
y> I don't see this as a problem, please explain...
PM> OSes (like NT on x86) uses ring 0 privileged level (the highest)
PM> for the microkernel and ring 1 (or 2) for the device drivers,
PM> file systems, network protkols, etc. User level progs are in
PM> ring 3.
That is almost completely wrong. Aside from the fact that Windows NT *isn't*
a microkernal operating system -- claims made in marketing literature
notwithstanding -- Windows NT is designed around a simple user/system
architectural split. (It wouldn't have been portable to Alpha and MIPS,
otherwise.) Windows NT on x86 doesn't use any rings other than rings 0 and 3.
I have yet to encounter *any* operating system for x86 processors that uses
ring 1. There are a few that use ring 2. IBM OS/2 Warp uses ring 2, for
example. But IBM OS/2 uses ring 2 merely to manage I/O port access in
application code. It doesn't have a microkernel and it doesn't use ring
protection to protect various non-user portions of the operating system from
one another in the manner that is described above.
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This archive was generated by hypermail 2b29 : Thu Jun 15 2000 - 21:00:31 EST