When the page containing a view of the list opens, the EnsureSSImporter function is called, which is defined in the OWS.JS file. This function creates the control on the page as follows:

new ActiveXObject("SharePoint.SpreadsheetLauncher.2")

Note:
In the context of an application whose version is earlier than Microsoft Office 2003, 1 is used as the version number.

When Office 2007 is installed on the client computer, this control is defined in the OWSSUPP.DLL file, a dynamic-link library (DLL) that is installed on the client during Office 2007 setup in the \\Program Files\Microsoft Office\OFFICE12 directory.