A VDDs can include a real-mode initialization procedure to query device state or to reserve portions of memory for use by the display adapter. For example, the initialization procedure should reserve any memory that corresponds to the display adapter's memory-mapped interface (if any). If the VDD supports multiple display adapters, the initialization procedure can check for the adaptors and indicate the result by returning a value in the EDX register. The VMM supplies this value as a parameter when the Sys_Critical_Init message is sent to the VDD.