;this code assumes that both DS and ES point to the correct segments.
cld
mov si,offset TestMessage
mov di,offset EmptyRam
mov cx,5  ;length of the source string, you'll need to either know this
          ;ahead of time or calculate it.
rep movsb
ret

;there is no buffer overflow protection built into these functions so be careful!
TestMessage byte "Hello"
EmptyRam byte 0,0,0,0,0