; DragonZap First Boot / Day 1. Educational example, MIT licence.
bits 16
org 0x7c00

start:
    cli
    xor ax, ax
    mov ds, ax
    mov es, ax
    mov ss, ax
    mov sp, 0x7c00
    sti
    cld

    mov ax, 0x0003      ; BIOS: clear screen, 80x25 text mode
    int 0x10
    mov si, message

.print:
    lodsb               ; read one byte from DS:SI into AL
    test al, al         ; zero marks the end of the message
    jz .halt
    mov ah, 0x0e        ; BIOS: print the character in AL
    xor bx, bx          ; display page 0
    int 0x10
    jmp .print

.halt:
    cli
    hlt
    jmp .halt

message db 'Hello from my first boot!', 0

times 510-($-$$) db 0   ; pad to the last two bytes
dw 0xaa55              ; boot signature: bytes 55 AA