Editing Device driver (section)

==Privilege levels==
Depending on the operating system, device drivers may be permitted to run at various different [[Privilege_(computing)|privilege levels]]. The choice of which level of privilege the drivers are in is largely decided by the type of [[Kernel (operating system)|kernel]] an operating system uses. An operating system that uses a [[monolithic kernel]], such as the [[Linux kernel]], will typically run device drivers with the same privilege as all other kernel objects. By contrast, a system designed around [[microkernel]], such as [[Minix]], will place drivers as processes independent from the kernel but that use it for essential [[input-output]] functionalities and to pass messages between user programs and each other.<ref>{{cite book
|last1=Tanenbaum
|first1=Andrew
|last2=Woodhull
|first2=Albert
|title=Operating Systems, Design and Implementation
|date=2006
|publisher=Pearson Pretence Hall
|location=Upper Saddle River, NJ
|isbn=0-13-142938-8
|page=256
|edition=3rd.}}</ref>
On [[Windows NT]], a system with a [[hybrid kernel]], it is common for device drivers to run in either [[CPU modes|kernel-mode]] or [[user space|user-mode]].<ref>{{cite book
|last1=Yosifovich
|first1=Pavel
|last2=Ionescu |first2=Alex
|last3=Russinovich
|first3=Mark
|last4=Solomon
|first4=David
|title=Windows Internals, Part 1
|date=2017
|publisher=Microsoft Press
|location=Redmond, Washington
|isbn=978-0-7356-8418-8
|edition=Seventh}}</ref>

The most common mechanism for segregating memory into various privilege levels is via [[protection ring]]s. On many systems, such as those with [[x86]] and [[ARM_(processor)|ARM]] processors, switching between rings imposes a performance penalty, a factor that operating system developers and [[Embedded software|embedded software engineers]] consider when creating drivers for devices which are preferred to be run with low latency, such as [[Network interface card|network interface cards]]. The primary benefit of running a driver in user mode is improved stability since a poorly written user-mode device driver cannot crash the system by overwriting kernel memory.<ref>{{cite web
 | url = http://blogs.msdn.com/iliast/archive/2006/10/10/Introduction-to-the-User_2D00_Mode-Driver-Framework.aspx
 | title = Introduction to the User-Mode Driver Framework (UMDF)
 | date = 2006-10-10
 | access-date = 2008-03-04
 | publisher = [[Microsoft]]
 | archive-date = 2010-01-07
 | archive-url = https://web.archive.org/web/20100107015247/http://blogs.msdn.com/iliast/archive/2006/10/10/Introduction-to-the-User_2D00_Mode-Driver-Framework.aspx
 | url-status = live
 }}</ref>