Basic sequential access method

In IBM mainframe operating systems, Basic sequential access method (BSAM) is an access method to read and write datasets sequentially. BSAM is available on OS/360, OS/VS2, MVS, z/OS, and related high-end operating systems.

BSAM is used both for devices that are naturally sequential, such as punched card readers, punches and line printers, and for data on devices that could also be addressed directly, such as magnetic disks. BSAM offers device independence: to the extent possible, the same API calls are used for different devices.