Index.dat File

In the Microsoft Windows Operating System, there is a file known as index.dat that is used by the Internet Explorer web browser. This file runs as long as Windows is running and acts as a repository for information such as webpages, search queries, and recently opened files. Its role is to allow the Internet Explorer to attempt to find an appropriate match when a user types in an edit field. Separate index.dat files exist for the Internet Explorer history, cache, and cookies.

A .dat filename extension is commonly used for a number of different types of data files, therefore you might encounter an index.dat file that has no relation to the Windows Operating System or to the Internet Explorer web browser.