HTTP Explained Page 2
The HTTP protocol uses the concept of reference provided by the Universal Resource Identifier (URI) as a location (URL) or name (URN), for indicating the resource on which a method is to be applied. When an HTML hyperlink is composed, the URL (Uniform Resource Locator) is of the general form http://host:port-number/path/file.html. More generally, a URL reference is of the type service://host/file.file-extension and in this way, the HTTP protocol can subsume the more basic Internet services.
The HTTP protocol is based on a request/response paradigm. The communication generally takes place over a TCP/IP connection on the Internet. The default port is 80, but other ports can be used. This does not preclude the HTTP/1.0 protocol from being implemented on top of any other protocol on the Internet, so long as reliability can be guaranteed.
After the server has responded to the client's request, the connection between client and server is dropped and forgotten. There is no "memory" between client connections. The pure HTTP server implementation treats every request as if it was brand-new, i.e. without context.
HTTP uses Internet Media Types (formerly referred to as MIME Content-Types) to provide open and extensible data typing and type negotiation. When the HTTP Server transmits information back to the client, it includes a MIME-like (Multipart Internet Mail Extension) header to inform the client what kind of data follows the header. Translation then depends on the client possessing the appropriate utility (image viewer, movie player, etc.) corresponding to that data type.