gtpa2m0d | Application Programming |
The main database of the TPF system is allocated at system generation time and is shared by all entries and all applications. It comprises two categories of file space. (A third category, general data sets, and a fourth, general files, are discussed in General Data Set and General File Support.)
The first category is analogous to a conventional multivolume data set organized for Basic Direct Access Method (BDAM). In the TPF system this organization is called fixed file storage. The second category is unique to TPF, and is termed random pool file storage. Random pool file storage (sometimes called pools) is similar to the areas of main working storage, because storage is dispensed and returned as needed. When an entry requests space in random pool file storage, TPF locates an available record and passes its address to the entry. The entry should record the address in a fixed file record because ultimately the system expects the requesting entry to release the random pool file record by returning the address to the TPF system. Data is stored and retrieved at the physical record level. The record size is fixed at 4096 bytes.
There is no TPF facility for allocating file storage dynamically. It is fixed at system generation time. Applications are not aware of the physical configuration of the files. Symbolic references and TPF facilities allow common access to the data by any application, and reconfigurations without reprogramming.