Details
BDAM requires that the file be allocated with DCB=DSORG=DA (direct access dataset organization) and SPACE=(,,CONTIG) (the file must be of fixed size with contiguous space). The file is opened output and all blocks are written sequentially to preformat the disk and optionally to load the data before the file can be used.
The programmer used the READ or WRITE macro instructions to access data, providing the block address and/or key. It was possible to start multiple input/output operations to run concurrently. The CHECK macro had to be used to wait for completion of a specific operation before the data could be accessed or the data buffer reused.
Read more about this topic: Basic Direct Access Method
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