Your DNS server will simply ask the root servers. Those are listed in a file (root.hint on BIND) and will tell you which server is authoritative for the TLD in

Your DNS server will simply ask the root servers. Those are listed in a file (root.hint on BIND) and will tell you which server is authoritative for the TLD in question. I'm not aware of any setups explicitly storing the TLD servers themselves (of course, they'll be in cache.)