wherein the first condition that requires a larger storage capacity of the storage unit in the document reading is a reading condition where {HEAD ~ a difference} is larger than {TAIL ~ an enough storage capacity} to implement the functions other than the image reading function, which difference is a storage capacity difference between: 
is larger than
wherein the first condition that requires a larger storage capacity of the storage unit in the document reading is a reading condition where { HEAD ~ a difference } is larger than { TAIL ~ an enough storage capacity } to implement the functions other than the image reading function , which difference is a storage capacity difference between :
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH