The 80286 microprocessor can be put into unreal mode only with help of the undocumented instruction LOADALL to modify the hidden segment base registers to point to the source or target memory location above 1 MiB.
[4] Starting with the 80386, real mode programs can use the 32 bit registers with the Address Size Override Prefix.
[13] 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.
[13] This mode is used in Grysztar's open-source FASM and Helix RM386, a commercial DOS Extender bundled by Logitech mouse drivers.