Basic, in IBM terminology, indicates a lower-level access method that deals with data sets in terms of physical blocks and does not provide either read-ahead, called anticipatory buffering, or synchronization — that is, the user program has to explicitly wait for completion of each input/output event.
In many applications, a hashing or randomizing function may be used to assign the block address based on a key in the data.
The programmer specifies DSORG=DA in his Data Control Block (DCB) to indicate use of BDAM.
Direct data sets must be preformatted before use by opening them as output and writing all the blocks sequentially.
[3] As a basic access method BDAM reads and writes member data in blocks and the I/O operation proceeds asynchronously and must be tested for completion using the CHECK macro.
[4] BDAM uses the standard system macros OPEN, CLOSE, READ, WRITE,and CHECK.
The READ or WRITE macro instructions must provide the block address or key of the desired record.