DNS is a hierarchical, decentralized system for mapping internet names to resources, most notably to IP addresses. It does this by designating authoritative name servers for each domain. Authoritative name servers can delegate authority over subdomains to other name servers. Thus, DNS provides both a form of decentralization and fault-tolerance.
From the earliest days of the internet, the idea of mapping easily-remembered names to less easily-remembered numbers (such as IP addresses). ARPANET used a text file called HOSTS.TXT (/etc/hosts on UNIX-based systems) that mapped hostnames to their numerical addresses. At the time, addresses were added manually.
Even when the list was relatively small, this manual system was cumbersome ...
