In this example, the ACB macro is used to identify a data set to be opened and to specify the types of processing to be performed. The access method control block generated by this example is built when the program is assembled.

BLOCK    ACB   AM=VSAM,BUFND=4,          BLOCK gives symbolic           x
               BUFNI=3,                  address of the access          x
               BUFSP=19456,              method control block.          x
               DDNAME=DATASETS,                                         x
               EXLST=EXITS,                                             x
               MACRF=(KEY,DIR,SEQ,OUT),                                 x
               STRNO=2

The ACB macro's parameters are:

• BUFND specifies four I/O buffers for data. BUFNI specifies three I/O buffers for index entries. BUFSP specifies 19456 bytes of buffer space, enough space to accommodate control intervals of data that are 4096 bytes and control intervals of index entries that are 1024 bytes.
• DDNAME specifies this access method control block is associated with a DD statement named DATASETS.
• EXLST specifies the exit list associated with this access method control block is named EXITS.
• MACRF specifies keyed-direct and keyed-sequential processing for both insertion and update.
• STRNO specifies two requests will require concurrent positioning.
• Since the type of resources are not specified, NSR is assumed.