## Physical Device Driver Reference

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### Direct Writing of GDT Selectors

Physical device drivers that set up GDT descriptors for private use will not work in OS/2 2.1. The solution is to use one of three Device Helper services - PhysToGDTSelector, PhysToUVirt or PhysToVirt. The decision about which service to use must be based on the context in which the memory is to be accessed.