Allocation of buffers for QSAM files

z/OS® DFSMS automatically allocates buffers for storing input and output for a QSAM file above or below the 16 MB line as appropriate for the file.

Most QSAM files have buffers allocated above the 16 MB line. Exceptions are:

  • Programs running in AMODE 24.
  • Programs compiled with the DATA(24) and RENT options.
  • Programs compiled with the NORENT option.
  • EXTERNAL files when the ALL31(OFF) runtime option is specified. To specify the ALL31(ON) runtime option, all programs in the run unit must be capable of running in 31-bit addressing mode.
  • Files allocated to the TSO terminal.
  • A file with format-S (spanned) records, if the file is any of the following ones:
    • An EXTERNAL file (even if ALL31(ON) is specified)
    • A file specified in a SAME RECORD AREA clause of the I-O-CONTROL paragraph
    • A blocked file that is opened I-O and updated using the REWRITE statement

related concepts  
Storage and its addressability