This procedure should only be needed if you are adding the Third+ controller or you are adding a 2nd controller with a non-standard memory address.
Use Regedt32 to navigate to:
On the Edit menu, Add Key name PARAMETERS with a blank Class. Select the PARAMETERS key and Add Key name <Controller Number> where <Controller Number> is a 1 if you are adding the second controller at a non-standard memory address. Otherwise, <Controller Number> is a 2. The Class for <Controller Number> is also blank.
Select the <Controller Number> key and Add Value the following names, as type REG_DWORD values:
BaseAddress - The physical address of the Data register for the controller.
DriveControl - The physical address of the drive control register of the controller. Often this is 0x206 off of the BaseAddress register.
Interrupt - The interrupt that the controller will use.