"Windows Search 4.0 is an updated component of Windows that enables instant search on your computer.

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.

Note The WS4 installation process automatically upgrades previous versions of Windows Search technologies."