程序代码：

    assume cs:code,ds:data
    data segment
    msg db 'Hello world!$'
    data ends
    code segment
start:
    mov  ax,data
    mov  ds,ax
    mov  ax,code1
    mov  es,ax
    xor  ax,ax
    push es
    push ax
    retf
    code ends
    code1 segment
    lea  dx,msg
    mov  ah,9
    int  21h
    mov  ax,4c00h
    int  21h
    code1 ends
    end start