WS4 lets you perform an instant search of your computer. WS4 helps you find and preview documents, e-mail messages, music files, photos, and other items on the computer. Please refer to the Knowledge base article KB940157 for a full description of the technology.
The WS4 installation process automatically upgrades previous versions of Windows Search technologies. Description of Windows Search 4.0 and the Multilingual User Interface Pack for Windows Search 4.0
Windows Search 4.0 - 64bit software