Windows Search, formerly known as Windows Desktop Search (WDS) on Windows XP and Windows Server 2003, is an indexed desktop search platform created by Microsoft for Microsoft Windows.
Windows Search collectively refers to the indexed search on Windows Vista and later versions of Windows (also referred to as Instant Search) as well as Windows Desktop Search, a standalone add-on for Windows 2000, Windows XP and Windows Server 2003 made available as freeware. All incarnations of Windows Search share a common architecture and indexing technology and use a compatible application programming interface (API).
Windows Search is the successor of the Indexing Service, a remnant of the Object File System feature of the Cairo project which never materialized. Windows Search uses a different architecture.
Windows Search builds a full-text index of files on a computer. (An add-in for 32-bit Windows XP, Windows Server 2003 and Windows Vista allows network shares to be added to the index.) The time required for the initial creation of this index depends on the amount and type of data to be indexed, and can take up to several hours, but this is a one-time event. Once a file’s contents have been added to this index, Windows Search is able to use the index to search results more rapidly than it would take to search through all the files on the computer. Searches are performed not only on file names, but also on the contents of the file (provided a proper handler for the file type is installed) as well as the keywords, comments and all other forms of metadata that Windows Search recognizes. For instance, searching the computer for "The Beatles" returns a list of music files on the computer which have "The Beatles" in their song titles, artists or album names, as well as any e-mails and documents that include the phrase "The Beatles" in their titles or contents.
Windows Search features incremental search search (also known as "search as you type"). It begins searching as soon as characters are entered in the search box, and keeps on refining and filtering the search results as more characters are typed in. This results in finding the required files even before the full search text is entered.
Windows Search supports IFilters, components that enable search programs to scan files for their contents and metadata. Once an appropriate IFilter has been installed for a particular file format, the IFilter is used to extract the text from files which were saved in that format.
Windows Search by default includes IFilters for common filetypes, including Word documents, Excel spreadsheets, PowerPoint presentations, HTML files, text files, MP3 and WMA music files, WMV, ASF and AVI video files and JPEG, BMP and PNG images. Windows Search uses property handlers to handle metadata from file formats. A property handler needs a property description and a schema for the property for Windows Search to index the metadata. Protocol handlers are used for indexing specific data stores. For example, files are accessed using File System Protocol Handler, Microsoft Office Outlook data stores using the Outlook Protocol Handler and Internet Explorer cache using the IE History/Cache Protocol Handler.
Windows Desktop Search was initially released as MSN Desktop Search, as a part of the MSN Toolbar suite. It was re-introduced as Windows Desktop Search with version 2, while still being distributed with MSN Toolbar Suite.
For Windows 2000, Windows XP and Windows Server 2003, it came in two flavors, one for home users and the other for enterprise use. The only difference between the two was that the latter could be configured via group policy. The home edition was bundled with MSN Toolbar, while the other was available as a standalone application. Later, when MSN Toolbar was discontinued in favor of Windows Live Toolbar, the home edition of Windows Desktop Search was discontinued as well. The last version available for Windows 2000 is Windows Desktop Search 2.66.
For Windows XP and Windows Server 2003, version 3.0 of Windows Desktop Search was provided as a standalone release – separate from Windows Live Toolbar. One of the significant new features is Windows Desktop Search 3.0 also installs the Property System on Windows XP introduced in Windows Vista. Windows Desktop Search 3.0 is geared for pre-Windows Vista users, hence the indexer was implemented as a Windows Service, rather than as a per-user application, so that the same index as well as a single instance of the service can be shared across all users – thereby improving performance. Windows Desktop Search found itself in the midst of a controversy on October 25, 2007 when Windows Desktop Search 3.01 was automatically pushed out and installed on Windows when updated via Windows Server Update Services (WSUS). Microsoft responded with two posts on the WSUS Product Team Blog.
Windows Search is the indexed search platform in Windows Vista, Windows 7 and Windows Server 2008, and offers a superset of the features provided by Windows Desktop Search, while being API compatible with it. Unlike WDS, it can seamlessly search indexed as well as non-indexed locations – for indexed locations the index is used and for non-indexed locations, the property handlers and IFilters are invoked on the fly as the search is being performed. This allows for more consistent results, though at the cost of searching speed over non-indexed locations. Windows Search uses Group Policy for centralized management.
Windows Search indexes offline caches of network shares, in addition to the local file systems, Microsoft Outlook e-mail stores and Microsoft OneNote stores indexed by WDS Windows Search also supports queries against a remote index. This means if the file server, on which a network file share is hosted, is running either Windows Vista or a later version of Windows or Windows Search 4.0 on Windows XP, any searches against the share will be queried against the server's index and present the results to the client system, filtering out the files the user does not have access to. This procedure is transparent to the user.
Unlike Windows Desktop Search on Windows XP, the Windows Search indexer performs the I/O operations with low priority, the process also runs with low CPU priority. As a result, whenever other processes require the I/O bandwidth or processor time, it is able to pre-empt the indexer, thereby significantly reducing the performance hit associated with the indexer running in the background.
Windows Search supports natural language searches; so the user can search for things like "photo taken last week" or "email sent from Dave". However, this is disabled by default. Natural language search expresses the queries in Natural Query Syntax (NQS), which is the natural language equivalent of AQS.