BSAM allows programs to read and write physical blocks of data, as opposed to the more powerful but less flexible Queued Sequential Access Method (QSAM) which allows programs to access logical records within physical blocks of data.
As a basic access method BSAM reads and writes member data in blocks and the I/O operation proceeds asynchronously and must be tested for completion using the CHECK macro.
[2] BSAM uses the standard system macros OPEN, CLOSE, READ, WRITE,and CHECK.
[2] If the dataset is unblocked, that is, the logical record length (LRECL) is equal to the physical block size (BLKSIZE), BSAM may be utilized to simulate a directly accessed dataset using NOTE and POINT on any supported direct access device type (DEVD=DA), and some primitive applications were designed in this way.
The BSAM application program interface can be compared with the interface offered by open, read, write and close calls (using file handles) in other operating systems such as Unix and Windows.