a to z of the digital world

A is for applet. This is not, despite the name, an offshoot of the computer company Apple, or an abbreviation from classified ads indicating an apartment to let. No, an "applet" is a small application program written in the new Java programming language, devised by Sun Microsystems.

The idea behind applets is that they will revolutionise the World Wide Web, the graphical portion of the Internet. At present, the Web can seem rather dull: you look at someone's home page, and there are some pictures and text. But what actually happens? Not a lot. It is not very interactive.

However, any picture downloaded from a Web page consists of thousands of bytes of data. Any half-decent programmer could write a program that would do something useful with that amount of space.

Hence applets. These are programs that are waiting to be loaded from a Web page when you click on them. Say, for example, you are looking at a financial services company's Web page and it is offering a special deal on mortgages. You want to work out what your repayments would be, given your particular financial circumstances. An applet is sent from the Web page to take up brief residence on your computer. You give it your financial details, and it sends those back to the original machine, which works out what your payments would be and sends the result back to you. The applet then wipes itself off your machine.

Applets can already be seen, by those with Windows 95 and Netscape 2.0, at the White House page (http://www.whitehouse.gov/) where the American flags "flutter".

You might wonder: isn't an applet rather like a virus? The answer is yes. But Sun says Java is carefully designed so that it cannot affect files or data on the machine it is sent to, without the user's explicit permission.