Appendix H

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Appendix H is the name of 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.

This NDAed documentation described various new features introduced in the Pentium processor, notably Virtual Mode Extensions (VME) and 4 MB paging (VME should not be confused with the later Intel VT virtualization technology). VME added an additional feature to the existing virtual 8086 mode that was introduced with the 80386 processor, and included optimized handling and delivery of interrupts to and from virtual machines.

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) and Christian Ludloff (owner of the website) played a major role in this.[1][2]

See also[edit]


  1. ^ Collins, Robert. "The Pentium's Enhanced v86 Mode",, January 1998. Retrieved on 26 December 2014.
  2. ^ Collins, Robert. "The Creation of Appendix H", Dr. Dobb's Journal, November 1997. Retrieved on 26 December 2014.