While receiving a disk drive reading command, the system processes the data saved in {HEAD ~ the free memory space} according to {TAIL ~ the disk drive reading command} 
While receiving a disk drive reading command , the system processes the data saved in { HEAD ~ the free memory space } according to { TAIL ~ the disk drive reading command }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL