Each physical record normally has a variable length physical record header, followed by data. However, certain records, following a record with a suitable header may have no header. The word length may be 16 or 32 bits but in both cases the values of lengths and pointers are in units of 16 bits.
The physical header identifier fields (7 and 8) are used by the off-line package to identify the header word length, to help in error detection and recovery, and to decide if byte swapping is required. For the 32 bit header words, the least significant 16 bits are in the leftmost 16 bits of the word, i.e. "IBM format". The off-line package achieves this by calling CTOIBM before the header is output.
: Physical Record Format
