QSAM arranges records sequentially in the order that they are entered to form sequential data sets, which are the same as those data sets that BSAM creates. The system organizes records with other records. QSAM anticipates the need for records based on their order. To improve performance, QSAM reads these records into storage before they are requested. This is called queued access. You can use QSAM with the following data types:

• sequential data sets
• basic format sequential data sets (before z/OS 1.7 these were known as sequential data sets or more accurately as non-extended-format sequential data sets)
• large format sequential data sets
• extended-format data sets
• z/OS UNIX files