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
NDA may stand for:
Military
* National Defence Academy (India), a military academy in India
* National Defence Act, legislation for organizing and funding Canada's military
* National Defense Academy of Japan, a military academy in Japan
* Nig ...
.
This NDAed documentation described various new features introduced in the Pentium processor, notably
Virtual Mode Extensions
In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a ...
(VME) and 4 MB
paging
In computer operating systems, memory paging is a memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory. In this scheme, the operating system retrieves data from secondary storag ...
. VME added an additional feature to the existing
virtual 8086 mode
In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running ...
(which was introduced with the
80386
The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors[Intel VT
x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU.
In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-as ...]
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
''Dr. Dobb's Journal'' (''DDJ'') was a monthly magazine published in the United States by UBM Technology Group, part of UBM. It covered topics aimed at computer programmers. When launched in 1976, DDJ was the first regular periodical focused on ...
'') and
Christian Ludloff (owner of the sandpile.org website) played a major role in this.
[Collins, Robert]
"The Creation of Appendix H"
, ''Dr. Dobb's Journal'', November 1997. Retrieved on 26 December 2014. From the Pentium Pro, the information in Appendix H was moved to the main documentation chapters, making the features publicly documented.
See also
*
Virtual 8086 Mode Enhancements
In the 80386 microprocessor and later, virtual 8086 mode (also called virtual real mode, V86-mode, or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a ...
(VME)
*
VME (CONFIG.SYS directive) VME may refer to:
Computing
* ICL VME, (Virtual Machine Environment) a mainframe computer operating system developed by International Computers Limited
* VMEbus, the ANSI/IEEE computer hardware bus standard
* Virtual machine escape is the process o ...
(in OS/2)
*
QEMM
Quarterdeck Expanded Memory Manager (QEMM) is a memory manager produced by Quarterdeck Office Systems in the late 1980s through the late 1990s. It was the most popular third-party memory manager for the MS-DOS and other DOS operating systems.
...
References
X86 architecture
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