This is Dennis Ritchie's Unix Assembler ("as"). Other PDP-11 assemblers include PAL-11R, PAL-11S and MACRO-11.

{{works with|UNIX|1}} to {{works with|UNIX|7}}

.globl  start
	.text
start:
        mov	$1,r0               / r0=stream, STDOUT=$1
	sys	4; outtext; outlen  / sys 4 is write
	sys	1                   / sys 1 is exit
	rts	pc                  / in case exit returns

	.data
outtext: <Hello world!\n>
outlen = . - outtext