Basic format data sets are sequential data sets that are specified as neither extended-format nor large-format. Basic format data sets have a size limit of 65 535 tracks (4369 cylinders) per volume. Basic format data sets can be system-managed or not. They can be accessed using QSAM, BSAM or EXCP.

You can allocate a basic format data set using the DSNTYPE=BASIC parameter on the DD statement, dynamic allocation (SVC 99), TSO/E ALLOCATE or the access method services ALLOCATE command, or the data class. If no DSNTYPE value is specified from any of these sources, then its default is BASIC.

Related reading: For more information on basic format data sets, see z/OS DFSMS Using Data Sets.