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The following discussion pertains to the FOCUS Database Server that performs all FOCUS data source I/O for the optional Simultaneous Usage (SU) facility.

The virtual storage requirements for this job consist of a fixed and a variable component. The fixed component is affected by the programs to be run under SU, and the variable component depends on the number of centrally controlled data sources and the number of TSO IDs or batch jobs to be serviced.

The fixed component is about 512K bytes. This accounts for all the programs that will be loaded, and for about 60 database buffers of 4096 bytes each. This is close to the default of 64 database I/O buffers FOCUS can manage.

The variable component needs 72 bytes per field in each centrally controlled data source, plus a maximum of 16000 bytes for each TSO ID or batch job that communicates with the central database job. This is a worst-case figure. A more likely average is about 6000 bytes per active user. The maximum would be needed, for example, in an installation with 20 concurrent users who will access 10 FOCUS data sources that have 100 fields apiece. Taking the highest possible number of bytes per user (16000 bytes), we get:

Fixed component	512,000 bytes
10 databases, 100 fields each	72,000 bytes
20 users, 16000 bytes each	320,000 bytes
TOTAL	904,000 bytes

Without more detailed information, the minimum virtual region for this job would be 960K. The recommended region is 50% greater, or 1440K. This increase is based on efficiency considerations and activity on the central database job itself.