Types of Snap-ins
If you're a system administrator, it's good to know which of the two types of plug-ins you are working with in the MMC for Windows XP. The two different types of snap-ins are defined here:
Stand alone snap-in. Provides management functionality even if alone in a console with no other supporting snap-ins. Snap-ins designed for this mode must not rely on any other snap-ins being present.
Extension snap-in. Provides functionality only when used in conjunction with a parent snap-in. An extension snap-in can extend only given node types. It declares itself as being a subordinate to nodes of certain types; for each occurrence of those node types in the console, the console adds the related snap-in extensions below it automatically.
For example, an extension snap-in might be a Log Pretty Print snap-in, providing users several ways to print out log files (such as the Windows 2000 Event Viewer log). With this snap-in installed, every log object in the namespace would be extended with the Pretty Print context menu item.
Extension snap-ins can provide a variety of functionality. Some actually extend the console namespace (for example, a snap-in that provides system information about computers would add that system information to the namespace under each computer in the namespace), whereas others simply extend context menus or specific wizards.
Many snap-ins support both modes of operation, offering some stand-alone functionality and also extending the functionality of other snap-ins. For example, the Windows 2000 Event Viewer snap-in reads the event logs of computers. If the MyComputer object exists in the console, the Event Viewer snap-in automatically extends each instance of a MyComputer object and provides the event logs for that computer. Alternatively, the event log can also operate in stand-alone mode, in which case an administrator must manually provide a computer name when the snap-in is opened, and the snap-in simply provides the event logs of this one computer.