what is ring0 and ring3 ??

what is ring0 and ring3 (in simple words, please) ??
I asked it in the C++ Programming Area, since I didn't knew where else I should ask it...
BOL_SNOTAsked:
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Karl Heinz KremerCommented:
The Intel (or compatible) i386 family CPUs have four different privilege levels: ring 0, 1, 2 and 3
Normal programs run in ring 3, which has a number of restrictions. Ring 0 is the level with the most privileges, you can basically do whatever you want with the CPU. The operating system runs in ring 0. Rings 1 and 2 are in between, again with different levels of privileges.
You can download the Intel IA-32 Intel Architecture Software Developer's Manual Volume 3: System Programming Guide (http://www.intel.com/design/Pentium4/manuals/25366813.pdf) and find more than you ever wanted to know about these protection rings. :-)
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MercantilumCommented:
Curiosity wise, have a look to

http://ftp.stratus.com/vos/multics/pg/mvm.html  ("Rings of Privilege" chapter)
http://www.multicians.org/mgr.html  (at "Ring ...")

Sounds like Intel got inspiration from this old good Multics OS, created in the 1960's ;-)
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BOL_SNOTAuthor Commented:
thanks, khkremer and Mercantilum.
you're comments where both very usefull, so I'll give you both 100 points.
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