What's the difference between plug-ins and helper applications?

Answer 1

A helper application is a separate application program that is invoked by the browser. It is simply a program that can understand and interpret files which the browser cannot handle by itself. Almost any program can be configured to act as a helper application for the browser. Examples of helper applications include Telnet and Excel.

The browser forks a separate process which starts the helper application. The helper application runs outside of the browser window. So, an advantage of helper applications over plug-ins is multitasking between a helper application and the browser window. If the browser is closed down, the helper application lives on.

Helper applications cannot display the contents of a file in the context of a Web page. If the file being read is a graphic, the helper application displays only the image, not the image embedded in the Web page. Another difference is that the browser has no control over the behavior of the helper application. The browser only has the ability to start the helper application and display the appropriate file.

whereas

A plug-in is an application program invoked by the browser. It is a dynamic code module designed to extend the capabilities of the browser by integrating a third party application program into the browser. Thus, a plug-in is part of the browser binary tree and runs inside the browser window. It cannot live on its own.

When plug-ins are installed they automatically tell the browser what file extensions they work with. Normally, there is no configuration involved with plug-ins, only installation. Because plug-ins are part of the browser binary tree they are platform specific. Therefore the correct version must be downloaded for plug-ins to work properly. Examples of plug-ins include RealAudio and Shockwave.