The I/O status block
(IOSB) for QIO functions on magnetic tape devices is shown in Figure 3-6. Appendix A lists the status returns for these functions.
(The OpenVMS system messages documentation provides explanations and
suggested user actions for these returns.) Table 3-2 (in “Magnetic Tape Driver Device Information”) lists the device-dependent data
returned in the second longword. The IO$_SENSEMODE function can be
used to return that data.
The byte count is the actual number of bytes transferred
to or from the process buffer or the number of files or blocks skipped.
(If an IO$_SKIPRECORD function is terminated by the detection of a
tape mark, the count returned in the IOSB is an unsigned number reflecting
the number of blocks skipped, plus 1.