You do not need 850 lines of code to output "hello world" unless you actually include a header. You could just stub printf instead of including and get it done with like 10 lines of code.

Assembly: Microsoft Macro Assembly "Hello World"

        .MODEL  TINY
        .CODE

CODE SEGMENT BYTE PUBLIC 'CODE' ASSUME CS:CODE,DS:CODE ORG 0100H DB 'HELLO WORLD$', 0 INC DH MOV AH,9 INT 21H RET

And then the interrupt calls into DOS code, which then calls into BIOS code, which then has the hardware do the work. The hardware itself will do stuff like translating instructions into microcode..