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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
Distributed Name Service. See DECdns.
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DNS(Domain Name System) The Internet's system for converting alphabetic names into numeric IP addresses. For example, when a Web address (URL) is typed into a browser, DNS servers return the IP address of the Web server associated with that name. In this made-up example, the DNS converts the URL www.company.com into the IP address 18.104.22.168. Without DNS, you would have to type the series of four numbers and dots into your browser to retrieve the website, which you actually can do. See IP address.
A Hierarchy of Servers
The DNS system is a hierarchy of duplicated database servers worldwide that begin with the "root servers" for the top-level domains (.com, .net, .org, etc.). The root servers point to the "authoritative" servers located in ISPs, as well as in large companies, that turn the names into IP addresses; the process known as "name resolution." Using our www.company.com example, COMPANY.COM is the domain name, and WWW is the hostname. The domain name is the organization's identity on the Web, and the hostname is the name of the Web server within that domain (see WWW). See DNS records, zone file, reverse DNS, recursive DNS, DDNS, HOSTS file, mDNS, ping, root server and WINS.
|Getting a Web Page|
|Converting the domain name (URL) in a Web browser into an IP address takes numerous queries. Along the way, there can be more name servers than are shown here.|
|Caching Speeds Up Delivery|
|If the ABC.COM Web address was previously requested by one of the ISP's customers, its IP address is cached (stored) in the DNS server and returns the IP address immediately. A user's computer also typically caches IP addresses, which can eliminate the DNS query all together if the address is already in the cache.|
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