Ajax

History

In the 1990's, web browsers and web sites lacked the sophistication to provide a quick and responsive user experience. Online form entry could be tedious, since all the requested information had to be entered and then submitted to the web server. The form data was validated and if there were problems, the same form was again presented to the user. The flow of information and the resulting experience was choppy and disconnected, reflecting the stateless nature of HTTP.

Asynchronous loading of content really became practical when Java applets were introduced in the first version of the Java language in 1995. These allow compiled client-side code to load data asynchronously from the web server after a web page is loaded. In 1996, Internet Explorer introduced the

Environment Variables in Windows XP

Environment variables are specially named aliases or placeholders for certain basic system properties that are present for convenience in programming and in system administration. Although they are mostly of interest to technical people, some can be useful to the average PC user and these are discussed here.

Environment variables have long been used in computer operating systems and are present in Unix, DOS, and Windows The word "environment" used in the context here refers to various features of the computer system and certain basic system data. Here is one of Microsoft's definitions:

Environment variables are strings that contain information such as drive, path, or file name. They control the behavior of various programs. For example, the TEMP environment variable specifies the location in which programs place temporary files.

Values for some of these variables are established at login and these are sometimes called predefined variables. They include