The disks are divided into sectors and each sector as {HEAD ~ a symbol} marking {TAIL ~ printed thereon} 
marking
The disks are divided into sectors and each sector as { HEAD ~ a symbol } marking { TAIL ~ printed thereon }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL