Four ring levels in x86 processor - only two are used, what is use of other two?

Question

There are four ring level 0,1,2,3 in x86 processors. However only two seem to be used.

• Ring level 0 - used for Operating system
• Ring level 3 - used for user application

I would like to understand what is use of other two levels?

Answer 1

Historically, processor architectures were rarely around for more than a decade or so. So general purpose operating systems traditionally don't have their core design based around any specific processor features. Having more than two privilege levels is an x86 oddity.