DNS or Domain Name System, helps resolve the name of any web address. When you type a domain name in your browsers address bar, say www.TheWindowsClub.com, your computer resolves this name into the IP address of the Internet server, where the site is hosted, using the Internet Protocol.
The Windows operating system, is set by default, to automatically use the DNS server of your ISP or Internet Service Provider.
A slow DNS server could be one cause for poor web browsing speed. If your ISP’s DNS server is slow, or responds slowly, or at times is overloaded, it may cause an additional delay of a few seconds, every time you go on to load a new web page.