This function is supported by the screen device driver. A 32-bit physical address and 16-bit length are passed to the physical device driver. The physical device driver returns an LDT selector for that area of memory.

Read/Write access is granted to any data areas completely contained in the range of addresses from A0000 to BFFFF. Read-Only access is granted for all other data areas completely contained in the range of addresses from 00000 to FFFFF. Requests for any other data areas result in a return code of ERROR_I24_INVALID_PARAMETER.

If the PhysToUVirt Device helper service returns a nonzero offset along with the requested selector, the selector is deallocated and ERROR_I24_INVALID_PARAMETER is returned. In this case, SCR_ALLOCLDTOFF should be used.