## Storage Device Driver Reference

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### Installation and Initialization

Filter device drivers are installed the same as adapter device drivers, using BASEDEV= statements in the CONFIG.SYS file of the workstation. In CONFIG.SYS, the filter device driver is loaded after any adapter device drivers it will control but before any device managers that the filter device driver will serve; this is ensured by use of the FLT file-name extension.

When the filter device driver receives its initialization packet from the kernel, it must scan the workstation's configuration to determine which units it wants to control, just as a device manager must when it initializes. A filter device driver uses the DevHlp_GetDOSVar to obtain a list of the entry points for all installed adapter device drivers, then it calls each ADD to obtain their device tables. The filter device driver must provide storage for these device tables.

Once the device tables are obtained, each is scanned by the filter device driver for units of interest. Having located the units of interest, the filter device driver must take one of the two actions previously listed, depending on whether the filter driver is using the permanent allocation method.