The well-known identifier __CLASS refers to a pseudo-property on every WMI object that indicates the class of the current object.
Use __CLASS in a WHERE clause to filter out any objects of derived classes from your result set. For example, the result set of the following query contains not only objects whose class is Win32_LogicalDisk, but also objects whose class is derived from Win32_LogicalDisk.
In the following example, the use of __CLASS in the WHERE clause filters out all objects of classes derived from Win32_LogicalDisk because their class is not Win32_LogicalDisk.
Use __CLASS in providers that are asked to provide instances of a specific class, irrespective of any subclasses.