To create new unique user accounts automatically by using Active Directory Domain Services (AD DS), you must enable Active Directory account creation mode.
Because at least one Central Administration Web application is required for each server farm, in the first server in the server farm, the Central Administration Web application is automatically installed and only one set of fields, for the Active Directory domain and the Active Directory organizational unit, are presented. When you run the configuration wizard on other servers in the farm, you will see the option on this screen to create the Central Administration Web application.
If you want to create a load-balanced URL for Central Administration or to provide redundancy, you can create more than one Central Administration Web site. However, in most installations this is unnecessary.
To enable Active Directory account creation modeWarning If you enable this option, you might not be able to upgrade from Microsoft SharePoint Foundation to other products based on SharePoint Products and Technologies. If you have trouble installing SharePoint products on this computer, run the SharePoint Products Configuration Wizard again to clear this option.