BTAM is a block-oriented access method for tape files of format BLKCTRL=NO. The following applies for block length: 18 bytes <= block length <= 32768 bytes (see description of the LEN operand in the BTAM action macro).
BTAM evaluates the FCB operand RECFORM. The specification of the record format is related to the block length.
RECFORM=F fixed length for blocks
The length is defined with BLKSIZE=length or is specified as LEN in the BTAM macro. The values specified above apply for the minimum and maximum length.RECFORM=U for blocks of undefined length
BTAM takes the block length either from the LEN operand in the macro or from the register specified in FILE/FCB with RECSIZE=reg.RECFORM=V for blocks of variable length
(record format V is treated as record format U)
Tape files created with SAM can be read block-by-block with BTAM. Since BTAM does not know the record structure, the user is responsible for deblocking the records.