In the example shown in Figure 1, the previously described data set is to be updated directly with transaction records on tape. The input tape records are 30 characters long, the key is in positions 1 through 10, and the update information is in positions 11 through 30. The update information replaces data in positions 31 through 50 of the indexed sequential data record.

Exclusive control of the data set is requested, because more than one task might be referring to the data set at the same time. Notice that, to avoid tying up the data set until the update is completed, exclusive control is released after each block is written.