What is protection rings in the PC architecture?

Question

The Peterson's solution to the critical section problem,

Init: flag[2]={False}  //two process problem
Init turn=i or j.
do {
flag [i] = TRUE;
turn= j;
while (flag[j] && turn==j);
critical section
 flag [i] = FALSE; 
remainder section
} while (TRUE);

hence there is no guarantee that this algorithm will work efficiently on Modern Architecture systems.(Ref:- Galvin Book Page No - 229 ), Why so, can somebody help me out?

Answer 1

Protection Rings

Protection Rings are concentric rings that provide strict boundaries and definitions for what the processes that work within each ring can access and what operations they can successfully execute.

The processes that operate within the inner rings have more privileges than the processes operating in the outer rings, because the inner rings only permit the most trusted components and processes to operate within them.

Protection rings support the availability, integrity, and confidentiality requirements of multitasking operating systems.

The most commonly used architecture provides four protection rings:

Ring 0 Operating system kernel

Ring 1 Remaining parts of the operating system

Ring 2 I/O drivers and utilities

Ring 3 Applications and user activity