The SAM access method permits the record formats: F (fixed record length), V (variable record length) and U (undefined record length).
When format U is used, SAM reads or writes only one record per data block (buffer). For example, the definition RECFORM=U in combination with BLKSIZE=STD and BLKCTRL=PAMKEY (is equivalent to RECORD-FORMAT=*UNDEFINED in combination with BUFFER-LENGTH=*STD and BLOCK-CONTROL-INFO in the ADD-FILE-LINK command) and a current record length of 48 bytes would mean that 2000 bytes in each PAM page would be “wasted”.
If the full capacity of a standard block is not used (e.g. after the action macro RELSE, SETL, FEOV or CLOSE), the remaining bytes in the block are unchanged, which means that their contents are undefined.
The size of the record must not exceed the block size.
For further information about record formats, see section “Record formats”.