To assemble "HELLOW", at the 'OS9' prompt enter:
ASM HELLOW #12K

To assemble "HELLOW" and generate an executable module in the "CMDS" directory,
at the 'OS9' prompt enter:
ASM HELLOW O #12K

To assemble "HELLOW" and generate a listing on the screen, at the 'OS9' prompt enter:
ASM HELLOW L #12K