The root server system is a set of thirteen file servers, which together contain authoritative databases listing all TLDs. Currently, NSI operates the "A" root server, which maintains the authoritative root database and replicates changes to the other root servers on a daily basis. Different organizations, including NSI, operate the other 12 root servers.(6) The U.S. Government plays a role in the operation of about half of the Internet's root servers. Universal name consistency on the Internet cannot be guaranteed without a set of authoritative and consistent roots. Without such consistency messages could not be routed with any certainty to the intended addresses.