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