;counts the length of a string
; in this case, we are using si as a pointer
        mov     si, 500h       ;position within the string (subscript)
        mov     cl,     0       ;counter to zero
lp:     cmp     byte ptr 0h [si], 0   ;eos????
        je      deend
        inc     si
        inc     cl
        jmp     lp
deend:  int     20h
        end