ORG     1600h

        USE16

        cli                             ; disable the interrupts, just in
                                        ; case they are not disabled yet

        lgdt    [cs:GDTR]               ; load GDT register

        mov     eax,cr0                 ; switch to protected mode
        or      al,1
        mov     cr0,eax

        jmp     CODE_SELECTOR:pm_start


NULL_SELECTOR = 0
DATA_SELECTOR = 1 shl 3                 ; flat data selector (ring 0)
CODE_SELECTOR = 2 shl 3                 ; 32-bit code selector (ring 0)
LONG_SELECTOR = 3 shl 3                 ; 64-bit code selector (ring 0)

GDTR:                                   ; Global Descriptors Table Register
  dw 4*8-1                              ; limit of GDT (size minus one)
  dq GDT                                ; linear address of GDT

GDT rw 4                                ; null desciptor
    dw 0FFFFh,0,9200h,08Fh              ; flat data desciptor
    dw 0FFFFh,0,9A00h,0CFh              ; 32-bit code desciptor
    dw 0FFFFh,0,9A00h,0AFh              ; 64-bit code desciptor

        USE32

pm_start:

        mov     eax,DATA_SELECTOR       ; load 4 GB data descriptor
        mov     ds,ax                   ; to all data segment registers
        mov     es,ax
        mov     fs,ax
        mov     gs,ax
        mov     ss,ax

        mov     eax,cr4
        or      eax,1 shl 5
        mov     cr4,eax                 ; enable physical-address extensions

        mov     edi,70000h
        mov     ecx,4000h shr 2
        xor     eax,eax
        rep     stosd                   ; clear the page tables

        mov     dword [70000h],71000h + 111b ; first PDP table
        mov     dword [71000h],72000h + 111b ; first page directory
        mov     dword [72000h],73000h + 111b ; first page table

        mov     edi,73000h              ; address of first page table
        mov     eax,0 + 111b
        mov     ecx,256                 ; number of pages to map (1 MB)
  make_page_entries:
        stosd
        add     edi,4
        add     eax,1000h
        loop    make_page_entries

        mov     eax,70000h
        mov     cr3,eax                 ; load page-map level-4 base

        mov     ecx,0C0000080h          ; EFER MSR
        rdmsr
        or      eax,1 shl 8             ; enable long mode
        wrmsr

        mov     eax,cr0
        or      eax,1 shl 31
        mov     cr0,eax                 ; enable paging

        jmp     LONG_SELECTOR:long_start

        USE64

long_start:

        mov     rax,'L O N G '
        mov     [0B8000h],rax

        jmp     long_start    

        org     100h

        cli

        push    0
        pop     es

        mov     di,1600h
        mov     si,basecode
        mov     cx,basecode_length
        rep     movsb

        jmp     0:1600h

basecode file 'BASECODE.BIN'
basecode_length = $ - basecode    

mov     al,10001b               ; begin PIC 1 initialization
out     20h,al
mov     al,10001b               ; begin PIC 2 initialization
out     0A0h,al    

Adam Kachwalla: There are 2 PIC's (ports 20h and 0a0h) needed to be initialized. It's not enough to initialize 1st PIC only and then use interrupts under 2nd PIC.

regards,
Mac2004

I think he means the redundant "mov al,10001b" below "out 20h,al".

MOV     AL,10001b
OUT     0x20,AL
OUT     0x0A0,AL    

MOV     RAX,'L O N G '
MOV     [0x0B8000],RAX
    

MOV RAX,"P n e u "
MOV [0x0B8000],RAX
MOV RAX,"m o n o "
MOV [0x0B8008],RAX
MOV RAX,"u l t r "
MOV [0x0B8010]
MOV RAX,"a m i c "
MOV [0x0B8018],RAX
MOV RAX,"r o s c "
MOV [0x0B8020],RAX
MOV RAX,"o p i c "
MOV [0x0B8010],RAX
MOV RAX,"s i l i "
MOV [0x0B8018],RAX
MOV RAX,"c o v o "
MOV [0x0B8020],RAX
MOV RAX,"l c a n "
MOV [0x0B8028],RAX
MOV RAX,"o c o n "
MOV [0x0B8030],RAX
MOV RAX,"i o s i "
MOV [0x0B8038],RAX
MOV RAX,"s "
MOV [0x0B8040],RAX    

Crikey! Writing one word takes up 24 lines of code... Imagine writing a Sentence, Paragraph, Essay or Thesis!