Unreal mode - WikiHQ

In x86 computing, unreal mode, also big real mode, flat real mode, or voodoo mode

32-bit code

The "huge real mode" (named in Ralf Brown's interrupt list) or "unREAL" mode (named by Tomasz Grysztar) adds the ability to run 32-bit code with a 4 GiB code segment. This is achieved by loading the code selector (CS) from a descriptor having the 32-bit attribute ("D" bit) set to 1. This mode allows for avoiding Operand Size Override prefixes normally required when using 32-bit addressing in 16-bit code segment, but is more difficult to set up due to interaction with interrupts.

[https://archive.org/stream/dr_dobbs_journal_vol_15/dr_dobbs_journal_vol_15_djvu.txt][https://archive.org/download/dr_dobbs_journal_vol_15/dr_dobbs_journal_vol_15.pdf] Errata: [https://www.drdobbs.com/letters/184408436]
(NB. Implements "Big real mode" SEG4G.)
Intel IA-32 Software Developer's Manual - Volume 3A
The Unabridged Pentium 4: IA32 Processor Genealogy, Addison Wesley . "Big real mode"
(xxvi+738+iv pages, 3.5"-floppy [https://web.archive.org/web/20190421200111/https://gopher.tildeverse.org/gopher.viste.fr/9/programming/PC/DOS/DOS%2520Internals/DOS_Internals.zip][https://web.archive.org/web/20200222111608/https://www.pcjs.org/pubs/pc/programming/DOS_Internals/]) Errata: [https://web.archive.org/web/20200222111742/http://www.geoffchappell.com/notes/dos/internals/][https://web.archive.org/web/20200222111853/https://gopher.tildeverse.org/gopher.viste.fr/1/programming/PC/DOS/DOS%2520Internals/crtdrvr][https://web.archive.org/web/20200222111945/https://gopher.tildeverse.org/gopher.viste.fr/1/programming/PC/DOS/DOS%2520Internals/xmswatch]
Method for expanding addressable memory range in real-mode processing to facilitate loading of large programs into high memory