# Appendix H

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{{primary sources|date=November 2015}}
'''Appendix H''' is an infamous appendix in Pentium Processor Family Developer's Manual, Volume 3. This appendix contained reference to documentation only available under a legally binding [NDA](/source/Non-disclosure_agreement).

This NDAed documentation described various new features introduced in the Pentium processor, notably [Virtual Mode Extensions](/source/Virtual_Mode_Extensions) (VME) and 4 MB [paging](/source/paging). VME added an additional feature to the existing [virtual 8086 mode](/source/virtual_8086_mode) (which was introduced with the [80386](/source/80386) processor), and included optimized handling and delivery of interrupts to and from virtual machines by reducing the number of traps required. VME should not be confused with the later [Intel VT](/source/Intel_VT) virtualization technology aiming at full virtualization of the CPU, rather than just the 8086 mode.

The appendix was referenced by the official chapters in the documentation, provoking irritation among the public who was not allowed to access the detailed descriptions.  This started a movement with observers trying to reverse-engineer the information in various ways. Notably, Robert Collins (writing in ''[Dr. Dobb's Journal](/source/Dr._Dobb's_Journal)'') and [Christian Ludloff](/source/Christian_Ludloff) (owner of the sandpile.org website) played a major role in this.<ref>Collins, Robert. [http://www.rcollins.org/ddj/Jan98/Jan98.html "The Pentium's Enhanced v86 Mode"], ''www.rcollins.org'', January 1998. Retrieved on 26 December 2014.</ref><ref>{{Cite web| last=Collins |first=Robert |date=Nov 1997 |title=The Creation of Appendix H |url=http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Website/articles/DDJ/1997/9711/9711n/9711ns1.htm |archive-url=https://web.archive.org/web/20141226024119/http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Website/articles/DDJ/1997/9711/9711n/9711ns1.htm |archive-date=2014-12-26 |access-date=2026-03-06 |journal=Dr. Dobb's Journal}}</ref> From the Pentium Pro, the information in Appendix H was moved to the main documentation chapters,{{which|reason=Which chapters?|date=March 2026}} making the features publicly documented.{{citation needed|date=March 2026}}

==See also==

* [Virtual 8086 Mode Enhancements](/source/Virtual_8086_Mode_Enhancements) (VME)
* [VME (CONFIG.SYS directive)](/source/VME_(CONFIG.SYS_directive)) (in OS/2)
* [QEMM](/source/QEMM)

==References==
{{Reflist}}

Category:X86 architecture

{{hardware-stub}}

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Adapted from the Wikipedia article [Appendix H](https://en.wikipedia.org/wiki/Appendix_H) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Appendix_H?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.