The Insert call

The standard insert (ISRT) call writes the data to the IMS Spool API using BSAM. Because the length of the data written to the spool can be up to 32760 bytes, the BSAM write is performed directly from the application program's buffer area.

If IMS finds that the user's I⁄O area is above the 16 MB line, IMS moves the user's application program data to a work area below the line before performing the BSAM write.

If the application area is already below the line, the write can be done directly from the I⁄O area. If possible, the I⁄O area should be below the 16 MB line. However, you do not need to take unusual steps to place the I⁄O area below the line unless performance shows that such action is necessary. By writing the application program's buffer without first moving it, IMS prevents problems associated with moving large blocks of data. When BSAM is used, change the format of the I/O area so that it contains the BSAM block descriptor word (BDW).

Related reading: For more information on the format of the I/O area, see IMS Version 15 Application Programming.