This article was previously published under Q322916
The Internet Explorer Index.dat file in the History folder may become very large over time.
The Index.dat file is never resized or deleted. Clearing the Internet Explorer history by clicking the Clear History button on the General tab in the Internet Options dialog box does not change the size of the Index.dat file. Also, setting the Days to keep pages in history value to 0 (zero) on the General tab does not change the size of the Index.dat file. The pre-allocated space in the Index.dat file increases Internet Explorer performance.
If the History folder becomes very large, it may cause reduced network performance if the folder is included as part of a roaming profile. A large History folder may also use a significant part of your profile quota. By default, the History folder is not included as part of a roaming profile in Microsoft Windows 2000 and Microsoft Windows XP. For additional information about how to exclude the History folder from roaming profiles in Microsoft Windows NT 4.0 and Microsoft Windows 98, click the article number below to view the article in the Microsoft Knowledge Base:
188692 How to Prevent Certain Folders from Uploading to Central Profile
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.
This problem does not occur with the Temporary Internet Files folder.