Alternatively, the data can be stored in fixed locations and {TAIL ~ the portals} moved from location to {HEAD ~ location} 
Alternatively , the data can be stored in fixed locations and { TAIL ~ the portals } moved from location to { HEAD ~ location }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD