Every device connected to the net has a unique, numerical IP address. These IP addresses are not human-friendly, though, so the Internet's designers added the Domain Name System (DNS}the hierarchical naming system that maps a more memorable URL to the actual IP address. The URL is a string of letters, numbers, and special characters, and each component has a specific meaning. The letters followed by the colon and forward slashes indicate the transmission protocol used to connect to the resource. The most common is Hypertext Transfer Protocol [http:i'r'), which specifies that the resource is a web page containing code the browser can interpret and display. Another is File Transfer Protocol (ftpz), which indicates that the resource is a file to be transferred. The last string is the top-level domain, which can indicate the type of organizaon or country code. The top-level domains \". Gov\" and \". Mil\" refers only to U.S. government agencies and military. There are also domain names for all two-letter country codes from the Ascension Islands (.ac) to Zimbabwe (.Zw). Alternatives to the overcrowded \". Com\" domain include \". Biz\" and \". Info\