To get things started, let's take a look an RPG program with a GUI interface in action.

So what is that chart showing?

The chart above shows the real-time "simulated" disk drive performance data from my i515 system. Your browser is requesting updated performance data from my i515 every second, via something known as an "AJAX" call. The chart is then updated with this new performance data.  

You may be wondering why I am using simulated disk drive performance data instead of the actual disk drive performance data.  Well, I certainly could have used the actual disk drive performance data from my system. But I wanted the first GUI example to be really interesting, and reach out and grab the reader.  Since the disk drives on my system are rarely ever busy, that would make for a really dull real time auto-refreshing chart.  If you dont believe me, go on to the next page, where the chart is showing the actual performance data from my server.