{TAIL ~ An actuator} moves {HEAD ~ a laser beam spot} to a desired track of an optical disk 
{ TAIL ~ An actuator } moves { HEAD ~ a laser beam spot } to a desired track of an optical disk
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH