;BIG UN/REAL MODE DYNAMIC GDT   ; 42 bytes NASM syntax olivier.poudade.free.fr 2010
	mov  byte [6000h],10h	; gdt descriptor gdt size nb:00*=base a00-a15,base a16-a23,segment access rights,limit 19:16+flags,base a24-a31
	mov  word [6002h],6006h	; gdt descriptor gdt address
	mov  word [600eh],0ffffh; gdt descriptor  segment limit
	mov  word [6013h],0cf92h; gdt descriptor cf=present,ring 0 DPL,data,expand-up,writable 92h=32-bit page-granularity
  	lgdt [6000h]          	; load gdt table
 	mov  eax,cr0          	; switch to pmode
xormode:xor  al,1               ; 1st=>set pmode bit LSbit=1(or al,1;switch to protected mode)
   	mov  cr0,eax            ; set control register 0 LSb
	push word 8            	; select descriptor 1 aka NULL descriptor entry 0 of Descriptor Table
	pop  ds                	; 8h = 1000b
	jp   xormode            ; PF=1=>set pmode bit LSbit=0(and al,0feh;back to real mode)
	mov  ds,bp        	; pop ds/restore big real mode @here bp=0 (from MBR entry register status) now DS can access 4gb
        mov  bx, 0x0f01         ; excluded from footprint / attrib+character
        mov  word [0x0b8000],bx ; excluded from footprint / 32-bit offset with default DS descriptor