Different levels software can be run at?

I really don't so..

Jeff Richter the author of many Windows 32 programming manuals taught me this in the Advanced Windows Hardware Architecture classes I took while I was working at Intel...

It is also in Helen Custer's Inside Windows NT..

Since Windows NT still has compatability with OS/2, all three rings would be used..

OS/2 Warp uses three rings.
ring3 - Application
ring2 - IOPL (ex Presentation Driver)
ring1 - not used
ring0 - Kernel, Physical/Virtual Driver

Originally Posted by ntwizard

I really don't so..

Jeff Richter the author of many Windows 32 programming manuals taught me this in the Advanced Windows Hardware Architecture classes I took while I was working at Intel...

It is also in Helen Custer's Inside Windows NT..

Since Windows NT still has compatability with OS/2, all three rings would be used..

Windows NT has limited compatibility with OS/2 (16 bit app only, no any privileged code like IOPL modules/dlls). OS/2 subsystem run only in Ring-3 like
VDM (DOS)