gtps4m0o | System Generation |
The organization of main storage for program and data manipulation is the key to the design of a high-performance system such as TPF. Storage protection is used for fixed storage to prevent an application from illegally modifying programs and critical data records (located in the global area). Part of main storage contains programs and data that are common to all entries and that always remain in main storage. This portion is called fixed storage or permanent core in TPF. Another portion, called working storage, is allocated to entries as required. Programs and data are transferred from file storage to working storage as required. Fixed storage consists of the following main storage areas:
Each individual area of both fixed and working storage will be expanded upon in later sections.
A general layout of main storage is provided in Figure 9. Starting from low core (shown at the bottom of the figure), each main storage area is addressed, up to the 16 megabyte line, by subsequent subsections of this chapter.
Algorithms are provided to calculate some system definition values.
The APSIZ parameter of the CORREQ macro relates to the overall layout of main storage. APSIZ specifies the size of the core resident programming areas above and below the 16M line.
The MDBF user will have to code multiple CORREQ macros, one for each subsystem. The non-MDBF user only codes one CORREQ macro.
Rather than calculate the sizes of the various areas by hand, users should make a rough pass at selecting the various main storage related SIP parameters.
Automatic resizing of the fixed storage areas takes place during an IPL.
Storage protection keys are included in the main storage layout in Figure 9. This provides a summary of storage sizes for the various mandatory and optional program and data areas in main storage. Values for the parameters may be calculated or estimated as explained in the accompanying sections. Actual sizes may be obtained from SIP Stage II listings and, for SNA support, the updated and assembled SNA keypoint (see data macro CK2SN).
Use of the word core as in core storage, core image, and so on, relates to the System/360 generation of computers. The correct terminology for System/370 and later systems is main storage. The words core and main storage are used interchangeably in this publication.
In the event of errors, or on request, TPF provides a system error dump of memory for the purpose of problem determination. The amount of storage dumped is controlled by using the commands ZDSER and ZASER. The amount of storage dumped can also be determined by the use of overrides created during the IPL (see the IDOTB macro in TPF System Macros and TPF Migration Guide: Program Update Tapes for more information) and by using the ZIDOT command.