You will have to set aside space in the prime area for track index entries. There will be two entries (normal and overflow) for each track on a cylinder that contains prime data records. The data field of each index entry is always 10 bytes long. The key length corresponds to the key length for the prime data records. How many index entries will fit on a track?

   Index entries per track = Track capacity / Length of index entries

Example: Again assuming a 3380 Model AD4 disk pack and records with 12-byte keys, 57 index entries fit on a track.

   Index     = 47968/(256+((12+267)/32)(32)+((10+267)/32)(32))
   entries   = 47968/832
   per track = 57