Privilege level
Encyclopedia
A privilege level in the x86 instruction set
controls the access of the program currently running on the processor to resources such as memory regions, I/O ports, and special instructions. There are 4 privilege levels ranging from 0 which is the most privileged, to 3 which is least privileged. Most modern operating systems use level 0 for the kernel/executive, and use level 3 for application programs. Any resource available to level n is also available to level 0..n, so the privilege levels are "rings
".
It is not necessary to use all four privilege levels. Existing software that was designed to use only one or two levels of privilege can simply ignore the other levels offered by the 80386 and later processors. A one-level system should use privilege level zero; a two-level system should use privilege levels zero and three. Here level zero is called the Supervisor mode while level three is User mode. All versions of Windows below Windows XP
use only the two-level system .
The real mode programs in 8086 are executed at level 0 (highest privilege level)whereas virtual mode in 8086 executes all programs at level 3.
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
controls the access of the program currently running on the processor to resources such as memory regions, I/O ports, and special instructions. There are 4 privilege levels ranging from 0 which is the most privileged, to 3 which is least privileged. Most modern operating systems use level 0 for the kernel/executive, and use level 3 for application programs. Any resource available to level n is also available to level 0..n, so the privilege levels are "rings
Ring (computer security)
In computer science, hierarchical protection domains, often called protection rings, are a mechanism to protect data and functionality from faults and malicious behaviour . This approach is diametrically opposite to that of capability-based security.Computer operating systems provide different...
".
It is not necessary to use all four privilege levels. Existing software that was designed to use only one or two levels of privilege can simply ignore the other levels offered by the 80386 and later processors. A one-level system should use privilege level zero; a two-level system should use privilege levels zero and three. Here level zero is called the Supervisor mode while level three is User mode. All versions of Windows below Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
use only the two-level system .
The real mode programs in 8086 are executed at level 0 (highest privilege level)whereas virtual mode in 8086 executes all programs at level 3.