HelloWorld in x86 assembly

Hello.asm

section .text
    global _start

section .data
msg db  'Hello, world!',0xa ;our dear string
len equ $ - msg         ;length of our dear string

section .text

; linker puts the entry point here:
_start:

; Write the string to stdout:

    mov edx,len ;message length
    mov ecx,msg ;message to write
    mov ebx,1   ;file descriptor (stdout)
    mov eax,4   ;system call number (sys_write)
    int 0x80    ;call kernel

; Exit via the kernel:

    mov ebx,0   ;process' exit code
    mov eax,1   ;system call number (sys_exit)
    int 0x80    ;call