The early internet's address book was a single text file kept in California.
Before 1983, every computer on the ARPANET found others using one file, HOSTS.TXT, maintained at the Stanford Research Institute. It could not keep up. Paul Mockapetris replaced it with the Domain Name System, a distributed hierarchy that now translates names like wikipedia.org into the numeric addresses computers actually use.
Computers find each other by numeric IP addresses, but people remember names. In the ARPANET days, the Stanford Research Institute kept a text file called HOSTS.TXT mapping every host name to its number; Elizabeth Feinler developed and maintained the first ARPANET directory there, while Jon Postel's team at the University of Southern California managed the numbers. By the early 1980s one central list, copied by everyone, had become slow and unwieldy.
Postel asked Paul Mockapetris to broker a compromise between five competing proposals. Mockapetris instead designed something new, the Domain Name System, published in 1983. Its key idea is delegation. Nobody holds the whole list. At the top are the root name servers; they point to servers for each top-level domain such as .org; those point to servers responsible for individual domains, and each domain's owner runs the final, authoritative answer.
Looking up www.wikipedia.org could, in principle, mean asking a root server, then the .org servers, then Wikipedia's own. In practice most lookups never reach the root, because answers are cached. Your home router and your internet provider remember recent answers for a period set by the domain's owner, known as the time to live, anything from seconds to weeks. That is why changes to a website's address can take a while to spread around the world.
The design has proved remarkably durable. DNS has been essential to the internet since 1985, and although its core rules were revised in 1987 it has since been extended to carry many kinds of records, from mail routing to security signatures. The phone-book analogy is common, but it undersells the achievement: it is a phone book with no single publisher, updated continuously by the owners of every domain.
Source: Wikipedia — Domain Name System · Text summarised from Wikipedia (CC BY-SA 4.0)
