## Presentation Device Driver Reference for OS/2

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### Default_Primary - Remarks

Action routines can perform whatever computation is necessary to modify the DSPINSTL data chain for eventual execution. Typically, action routines modify a key field within a data element, or they might add or subtract chain elements.

Generally, action routines should not change external system values such as OS2.INI entries because there is no guarantee that the user will not end the installation process after the action routine returns. Therefore, persistent state setting should be performed by the commands within DSP files rather than by action routines.

The action routine communicates with the DSPINSTL utility program by setting the data chain element key values. Therefore, if an action routine sets several alternative key values in different chain elements, an equivalent set of DSP files (at least one for each alternative key value) must be provided in the eventual source directories or diskettes. (See DSPINSTL Service Functions).