URLs Uniform Resource Locators, or URLs, are designed to provide a standard format by which to point to a file. The file may exist on any network-accessible machine the browser has access to, and files may be accessed using a variety of protocols. Probably the most common protocols are http, file, gopher, and ftp. The http protocol indicates that the browser should contact the server using the hypertext transport protocol, which is used by servers designed to serve HTML documents. The file protocol is used to retrieve a file from a local directory.
Many browsers also support an ftp protocol for retrieving non-local files using anonymous ftp.
The gopher protocol is used to retrieve documents from a gopher server. The host.domain is the host and domain name of the remote server to contact in order to retrieve a document. If the document is on the local system, you can create a partial URL that does not specify the host.domain. This option is often omitted since most remote services will be provided at a well-known port on the remote system. For instance, the http protocol is commonly found on port 80, while gopher is found on port 70.