If the DNS server does not know the address of the requested site, then it will forward the request to another DNS server. In order to do so, the DNS server must know of the IP address of another DNS server that it can forward the request to. This is the job of root hints. Root hints provides a list of IP addresses of DNS servers that are considered to be authoritative at the root level of the DNS hierarchy(also known as root name server).
The good news is that root hints are preconfigured on Windows Server 2003 DNS servers. The root hints are stored in a file named cache.dns that is located in the \Windows\System32\Dns folder. If you would like to see what the root hints file looks like, you can open it in Notepad. The root hints file is really nothing more than just a text file that pairs root DNS servers with their IP addresses.