Program Specification Block

program specification block
(PSB) defines all of the database views that are available to an application. A PSB consists of one or more PCB definitions similar to the one shown in Figure 18. One PSB can contain up to 255 separate PCBs.
For each PCB you define, you must include the PSBGEN statement. The PSBGEN statement names the PSB and specifies the language in which the current applications are written.
Parallel Processing
If a PSB contains multiple PCBs, an application using the PSB can engage in parallel processing. Since each PCB can reference a separate DBD, the application, by way of multitasking, can perform parallel processing on different databases or on different views of the same database. DL/I maintains a separate PCB control block for each database in use.