The web server sends a piece of information before sending a file to your web browser client,

The browser then looks at this data and decides if it can handle it internally; for example, if the server sends image/jpeg, the browser will happily support this by displaying the image within it's own internal window.

However, if it receives audio/mpeg, it looks at its mime types file to see what application it needs to spawn to view the file. If the file type doesn't exist in the server's mime.types file, it will not send this valuable data, and the browser will attempt to load the file into its own internal window.

The main difference between the Amiga's data handling and other operating systems is that the Amiga will look at a signature file in the datatypes directory and try to match it to the first few bytes of the file.

This is how Amiga datatypes decide out how to display data, so if you save a gif file with an extension of .jpeg, or no extension at all, the Amiga still knows that the file is a gif file, provided you have a gif.datatype installed in your system.

Other platforms simply look at the file extension to determine how to handle the data.