The Unabridged Pentium 4 IA32 Processor Genealogy

Registers Accessible in Real/VM86 Mode

A program operating in Real Mode or VM86 Mode has access to:

• All of the 8086 registers,

• as well as the two additional data segment registers—FS and GS.

The FS and GS segment override prefixes may be used. As an example:

mov  ah,  fs:[0100] ;read byte from location 0100h in fs
                    ;data segment into ah register

In addition, the following MMX/SSE/SSE2-related registers are also accessible:

• MMX registers (MMX[7:0]).

• XMM data registers (SMM[7:0]).

• MXCSR.