After you have determined how your data set is to be organized, you must consider how the individual records will be referred to when the data set is updated or new records are added. You refer to records using one of three forms of addressing:

• Relative Block Address. You specify the relative location of the record (block) within the data set as a 3-byte binary number. You can use this type of reference only with format-F records. The system computes the actual track and record number. The relative block address of the first block is 0.
• Relative Track Address. You specify the relative track as a 2-byte binary number and the actual record number on that track as a 1-byte binary number. The relative track address of the first track is 0. The number of the first record on each track is 1.

  Direct data sets whose records are to be identified by relative track address must be limited in size to no more than 65 536 tracks for the entire data set.

• Actual Address. You supply the actual address in the standard 8-byte form, MBBCCHHR. Remember that using an actual address might force you to specify that the data set is unmovable. In that case the data set is ineligible to be system managed.