gtps4m14 | System Generation |
General data sets are usually related to some offline processing. Data is either produced online (for example, management reports) to be processed by offline (MVS) programs; or data is produced offline for online processing. A general data set provides a data interface between the offline and online system components.
A TPF general data set (a disk module) is directly related to the meaning of an MVS data set. The records of a data set are allocated sequentially within the same module (volume in MVS). The file is processed online by using the FIND and FILE macro requests. A special macro, file data chain transfer (FDCT), permits the processing of records that are not restricted to the standard TPF file record sizes. A file with standard record sizes is processed online by using the TPF standard FIND and FILE macro requests. The file referencing is slightly different from the procedures used to access fixed record types and pool records.
Two distinct general data set macros are provided to allow an ECB controlled program to access records within a general data set:
A command is provided to allow a system operator to mount and dismount volumes associated with a data set. The TPF general data set volumes are formatted by offline MVS utilities. The formatter program produces a header called a volume label. Volume labels are used to identify MVS compatible data sets. See the TPF Database Reference for more information about general data set support.
The SIP RAM macro parameter GSON is used to specify the number of slots (spindles not required for online modules) in the DASD file status table. General data sets are mounted on these spare spindles. The spare slots in the file status tables are used to control them.
All general data set control records are obtained from fixed file records accessed through the FACE program. The SIP RAMFIL macro is used to allocate these records. They are obtained and returned as needed and may be used at any point in time for any of the data set control records. Therefore, the total number of data set records required will vary with the number of data sets to be mounted, the DASD device type and the number of volumes within a data set, and the number of loosely coupled processors.
Data set records must be allocated as 1055-byte records. The size and number of records to be allocated is described in macro DSEQU.