Under Windows, the standard 31 priorities of the Ada model are mapped onto Window’s seven standard priority levels by default: Idle, Lowest, Below Normal, Normal, Above Normal,
When using the FIFO_Within_Priorities task dispatching policy, GNAT
assigns the REALTIME_PRIORITY_CLASS priority class to the application
and maps the Ada priority range to the sixteen priorities made available under
REALTIME_PRIORITY_CLASS.
For details on the values of the different priority mappings, see declarations
in system.ads. For more information about Windows priorities, please
refer to Microsoft documentation.