Domain Name System (DNS) servers are used to resolve hostnames to IP addresses. Name resolution makes it easier for people to access other IP hosts. For example, do you know what the IP address is for Google? No? Do you know the hostname of Google server? Yes, you would use www.google.com. From your computer, pinging www.google.com actually sends the request to 66.102.1.147, the IP address returned by your DNS server.

You can understand why many people might not know the IP address but would know the domain hostname. Windows 7 asks the DNS server configured on the machine for the resolution of the hostname to an IP address. Most companies and Internet service providers (ISPs) have their own DNS servers that know how to resolve any valid request. There are public DNS servers that can be used as well.