When you click on an IGB icon, IGB is downloaded from our site and run on your computer.
This is done through a mechanism called Java Web Start, which allows software applications to be downloaded and started by your Web browser. If your computer is relatively up-to-date, the software you would need to launch IGB using Java Web Start is probably already installed and ready to work.
What happens "behind the scenes" is that when you click an IGB icon, your browser downloads a "JNLP" file, short for Java Network Protocol. JNLP files just contain instructions telling your computer how to obtain and launch a particular software program - like IGB - from over the Web.
When you click the IGB icon, your Web browser downloads the JNLP file. The Java Web Start mechanism then "reads" the JNLP file, figures out where to get IGB (from the Bioviz site) and then starts the download. Once the download finishes, IGB will launch.
Because it's inefficient to download the entire software program each time you want to use it, Java Web Start saves the software it downloads in a special directory (a "cache") dedicated to this purpose. However, each time you launch IGB, Java Web Start will check the Bioviz site to see if there are any new versions available for the download. If there are, it downloads and launches the newer version. As a result, the software on your local computer stays up-to-date with the current release of IGB.
Wikipedia Entry for Java Web Start