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'''System Management Mode''' ('''SMM''', sometimes called '''ring −2''' in reference to [[protection ring]]s)<ref>{{cite web | url=https://www.blackhat.com/docs/us-15/materials/us-15-Domas-The-Memory-Sinkhole-Unleashing-An-x86-Design-Flaw-Allowing-Universal-Privilege-Escalation-wp.pdf | title=The Memory Sinkhole | date=20 July 2015 | accessdate=22 August 2015 | author=Domas, Christopher |publisher = [[Black Hat Briefings|Black Hat]]}}</ref><ref>{{cite web | url=https://www.blackhat.com/presentations/bh-usa-09/TERESHKIN/BHUSA09-Tereshkin-Ring3Rootkit-SLIDES.pdf | publisher=[[Invisible Things Lab]], [[Black Hat Briefings|Black Hat USA]] | date=29 July 2009 | accessdate=22 August 2015 |author1=Tereshkin, Alexander |author2=Wojtczuk, Rafal |title=Introducing Ring -3 Rootkits |page=4 }}</ref> is an operating mode of [[x86]] [[central processor unit]]s (CPUs) in which all normal execution, including the [[operating system]], is suspended. An alternate software system which usually resides in the computer's [[firmware]], or a hardware-assisted [[debugger]], is then executed with high privileges.
It was first released with the [[Intel 386SL]].<ref>{{cite web|url=http://blogs.msdn.com/carmencr/archive/2005/08/31/458609.aspx|title=SMIs Are EEEEVIL (Part 1)|publisher=Microsoft|work=msdn.com|date=17 July 2020 }}</ref><ref>Ellis, Simson C., "The 386 SL Microprocessor in Notebook PCs", Intel Corporation, Microcomputer Solutions, March/Apri 1991, page 20</ref> While initially special SL versions were required for SMM, Intel incorporated SMM in its mainline 486 and Pentium processors in 1993. [[AMD]] implemented Intel's SMM with the [[Am386]] processors in 1991.<ref>{{cite web | url=http://pdf.datasheetcatalog.com/datasheet/AdvancedMicroDevices/mXwtys.pdf | title=AMD Am386SX/SXL/SXLV Datasheet|publisher=AMD}}</ref> It is available in all later [[microprocessor]]s in the x86 [[Computer architecture|architecture]].{{citation needed|date=December 2021}}
In [[ARM architecture]] the Exception Level 3 (EL3) mode is also referred as Secure Monitor Mode or System Management Mode.<ref>https://documentation-service.arm.com/static/5ed11e40ca06a95ce53f905c?token= {{Bare URL PDF|date=March 2022}}</ref>
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