On the Internet, the root server system is the way that an authoritative master list of all top-level domain names (such as com, net, org, and individual country codes) is maintained and made available to all routers.

The system consists of 13 file servers. The central or "A" server is operated by Network Solutions, Inc., the company that originally managed all domain name registration, and the master list of top-level domain (TLD) names is kept on the A server.
On a daily basis, this list is replicated to 12 other geographically dispersed file servers that are maintained by an assortment of agencies. The Internet routing system uses the nearest root server list to update routing tables.