DNS Servers (Domain Name Servers) provide a friendly name to IP address resolution. In other words, if you type www.brighthub.com, this URL (or address) is translated by your ISP (Internet Service Provider) from www.brighthub.com to 66.165.142.74. This makes life easy as an Internet user. Without DNS Servers, you would have to write down every IP address of every website you were going to visit.
Below is an example of how DNS works (note the ip address in the address line). After opening Internet Explorer, enter the IP address and hit enter. You will instantly be transported to your destination. This actually is faster (going to a website) than typing the address. Remember, if the address is typed, Internet Explorer, Firefox and all other browsers take the request to the DNS server where the 'name' is traded out for the IP address. Packets are then routed from router to router until your website is returned.

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DNS Servers have databases and relay to one another the information that is in them. With a few root servers in the world, websites that are purchased (www.yournewdomain.com) are entered into these servers where the name and IP address are registered together. These servers then talk with other DNS servers so that web browser requests that come in will be translated to the IP address.