What Are Root Hints?

Root hints are a list of 13 FQDN Your DNS server, whether it is on the Internet Unable to resolve the DNS query or by using its Own zone data , DNS forwarding, or their Cache . Root hints listed in the highest server DNS hierarchy, and can provide DNS server information needed Iterative query execution to the next lowest DNS name space layer. 

Root servers are automatically installed when you install the DNS role. They are copied From Cache.dns file is included in said DNS role installed files. You can also add the root Tip DNS server to support non- contiguous domain in the forest to find.