| Revision as of 10:34, 2 October 2016 editMaxime Vernier (talk | contribs)Extended confirmed users4,235 editsm Add a link to call gate← Previous edit | Revision as of 13:41, 9 November 2016 edit undo2.190.6.58 (talk) some extra information about why there is two privilege levelTag: Visual editNext edit → | ||
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| A '''privilege level''' in the ] ] 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 "]". When a lesser privileged process tries to access a higher privileged process, a General Protection Fault is reported by the OS. | A '''privilege level''' in the ] ] 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 "]". When a lesser privileged process tries to access a higher privileged process, a General Protection Fault is reported by the OS. | ||
| It is not necessary to use all four privilege levels |
It is not necessary to use all four privilege levels, Because the current ] like Windows, Linux , etc. mostly are using ] mechanism and Paging only has one bit to specify the privilege level which is either Supervisor or User (U/S Bit). ] uses the two-level system.<ref>Russinovich, Mark E.; David A. Solomon (2005). Microsoft Windows Internals (4 ed.). Microsoft Press. pp. 16. ISBN 978-0-7356-1917-3</ref> | ||
| 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.<ref>Sunil Mathur, "Microprocessor 8086: Architecture, Programming and Interfacing" , Eastern Economy Edition, PHI Learning</ref> | 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.<ref>Sunil Mathur, "Microprocessor 8086: Architecture, Programming and Interfacing" , Eastern Economy Edition, PHI Learning</ref> | ||
Revision as of 13:41, 9 November 2016
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". When a lesser privileged process tries to access a higher privileged process, a General Protection Fault is reported by the OS.
It is not necessary to use all four privilege levels, Because the current Operating Systems like Windows, Linux , etc. mostly are using Paging mechanism and Paging only has one bit to specify the privilege level which is either Supervisor or User (U/S Bit). Windows NT uses 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.
See also
References
- Russinovich, Mark E.; David A. Solomon (2005). Microsoft Windows Internals (4 ed.). Microsoft Press. pp. 16. ISBN 978-0-7356-1917-3
- Sunil Mathur, "Microprocessor 8086: Architecture, Programming and Interfacing" , Eastern Economy Edition, PHI Learning
- Intel 80386 Programmer's Reference