gtpd1m0i | Database Reference |
The general data set (GDS) support allows a TPF application to read and write MVS BSAM or QSAM DASD data sets that are used to pass data between MVS and TPF. General data sets are BSAM or QSAM multivolume fixed-length record data sets with records in TPF sizes (381, 1055, 4095, or 4096 bytes). The GDS support allows the use of nonstandard record sizes up to 4096, but the user must handle the record accessing using either FDCTC or FNSPC/FLSPC macros.
The GDS support does not include the ability to create or expand a data set; all space allocation and formatting must be done on MVS. The GDS support does include the ability to display all mounted data sets by data set name (DSNAME) or data definition name (DDNAME), and the ability to scan the volume table of contents (VTOC) for a specific data set name or to display all data sets with extents on the volume. Also included in the GDS support is the ability to automatically premount a set of data sets and the ability for the system to automatically remount previously mounted data sets during a system restart. It extends the use of the find and file macros to these general data sets (referred to as data sets in the remainder of this chapter), allowing for TPF single record processing of this data.
Despite the similarity in names, general data sets are not related in any way to general file data sets. General file data sets are designed for use solely by TPF systems for such varied purposes as:
General files are discussed in General Files.
The physical attributes of general data sets are as follows:
Functions provided by this general data set facility are:
Multivolume data sets can be accessed as follows:
Data sets with multiple extents appear as a single contiguous extent on that volume on which the data set resides.