boot.s

   1         bits 16 ; boot sectors run in real mode
   2         org 7c00h ; boot sector is always loaded at 0x7c00
   3
   4         mov al, 1 ; update cursor after write
   5         mov bh, 0 ; write to page 0
   6         mov bl, 00000111b ; attribute: high nibble is foreground (light gray),
   7                                           ; low nibble is background (black)
   8                                           ; NOTE: in the binary, these will be inverted, so low nibble here will become high nibble in binary and vice versa!
   9         mov cx, msg1end - msg1 ; size of message
  10         mov dl, 0 ; column to write to
  11         mov dh, 0 ; row to write to
  12         push cs ; push code segment to stack
  13         pop es ; pop pushed code segment to extra segment, this serves as the base to the string
  14         mov bp, msg1 ; offset where the string is
  15         mov ah, 13h ; write string subservice
  16         int 10h ; call BIOS interrupt 0x10
  17         jmp msg1end ; jmp to endless loop
  18         msg1 db "Gotta start somewhere"
  19         msg1end: jmp msg1end
  20
  21         times 510-($-$$) db 0 ; fill with 0 until 0x1fc is reached
  22         dw 0xaa55 ; BIOS MBR signature