Program that boots an emulator/computer from a floppy and prints 'Hello, world.'

hello.asm

[bits 16] ; Tell assembler to use 16 bit code.
[org 7c00h] ; BIOS will load us to this address.

;===================================================================
mov si, string_hello ; store string pointer into SI
call print_string
call sleep

;===================================================================
print_string:
;expect pointer to string's beginning to be in SI
    next_character:
    mov al,[si] ; gets a byte from string and stores in AL
    inc si ; increment si pointer
    or AL, AL ; check if value in AL is zero (end of string)
    jz exit_print_string ; if end of string, exit
    call print_character ; else print character in AL
    jmp next_character
    exit_print_string:
    ret

;===================================================================
print_character:
;expect ASCII value of character to be printed in AL
    mov ah, 0x0e ; teletype mode, sets BIOS to print one character
    mov bh, 0x00 ; page number
    mov bl, 0x07 ; text attribute (light gray on black)
    int 0x10 ; BIOS video interrupt
    ret ; return to calling procedure

;===================================================================
sleep:
    hlt ; halt cpu till next instruction
    jmp sleep ; loop forever

;===================================================================
string_hello db 'Hello, world.', 0 ; string ending with 0

;===================================================================
times 510 - ($-$$) db 0 ; fill rest of the sector with 0
dw 0xaa55 ; add boot signature to mark as bootable.

run.sh

#!/bin/bash

# Usage: ./run.sh hello.asm
# Assumes you have nasm and Q.app installed.

dd if=/dev/zero of=floppy.img bs=512 count=2880
nasm $1 -o binary.out
dd if=binary.out of=floppy.img conv=notrunc
/Applications/Q.app/Contents/MacOS/i386-softmmu.app/Contents/MacOS/i386-softmmu -hda floppy.img