The basic sequential access method (BSAM) and basic partitioned access method (BPAM) provide the READ, WRITE and TRUNC macros for transmitting data between virtual and auxiliary storage. These macros can be issued in 24- or 31-bit addressing mode. Macros are provided to help you manage buffers, or to do overlapped I/O.

The READ and WRITE macros process blocks, not records. Thus, you must block and unblock records. Buffers, allocated by either you or the operating system, are filled or emptied individually each time a READ or WRITE macro is issued. The READ and WRITE macros only start I/O operations. To ensure the operation is completed successfully, you must issue a CHECK, WAIT, or EVENTS macro to test the data event control block (DECB). The only exception is that, when the SYNAD or EODAD routine is entered, do not issue a CHECK, WAIT, or EVENTS macro for outstanding READ or WRITE requests.