Referring to FIG 19, three block groups 1902, 1904, and 1906 are shown as {HEAD ~ linked lists} of {TAIL ~ blocks} 
Referring to FIG 19 , three block groups 1902 , 1904 , and 1906 are shown as { HEAD ~ linked lists } of { TAIL ~ blocks }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL