Some great information here about evolution search at Microsoft by JT, really good read here.
Indexing Filters, or more commonly shortened to IFilters, play an important role in Microsoft’s Search technology starting with Indexing Server 1.0 on Windows NT 4.0 (see “Anatomy of a Search Solution”) and have been enhanced and added to by not only Microsoft, but by many 3rd party independent developers and software vendors (ISV’s). Many of the IFilters are free or relatively low cost and cover many file types formats or extensions. IFilters are an established and open standard that is documented on Microsoft’s MSDN and code examples and utilities are available in Microsoft’s Platform SDK (PSDK).
Recently due to the new MSN Desktop Search tool, there has been an explosion of interest in IFilters as the MSN Toolbar Suite with Desktop Search uses this same IFilter technology as does MS SQLServer Full Text Search (FTS) when third party IFilters such as Adobe’s PDF file type is stored in SQL Server. Exchange, SharePoint and Windows XP Indexing Service all use Index Filters as well. In my humble opinion, Index Filters are Microsoft’s "secret weapon" in Search Engine wars with Google, Yahoo, X1 and other Desktop Search tools as they most often rely on another 3rd party vendor (Stellent) to provide access to many, but limited set of file types. Additionally, these desktop and commercial search engine tools are limited to only what Stellent’s Outside In Technology can provide and are not extensible as IFilters are.
Interestingly, other software vendors, such as Oracle Text also uses Stellent’s Outside In Technology. Furthermore, the Google Mini Search Appliance supports searching in 220 file formats, which is approx. the same number of file formats supported by Yahoo’s X1 for their desktop search. I am not surprised by this as I’m sure that many other search vendors are using the Outside In technology from Stellent.
More importantly for Desktop Search and consumers, and to the explosion of interest in using MSN Desktop Search to full text index multiple file types, and understanding what IFilters are installed has difficult to determine. Now, along comes IFilter Explorer 1.0 (or an IFilter Viewer) from Citeknet that dramatically improves how to determine what IFilters are installed on your system. The IFilter Explorer also has tabs that can group IFilters by application, specifically – MSN Desktop Search, SQL Server 2005, SharePoint, WSS / SQL Server 2000, Win32 API / Indexing Service 3.0 and Indexing Service 2.0. Furthermore, the IFilters can be gr