Index.Dat Files and Primary I.E. Folders

from the author of 

PurgeIE - Purge Cache, Cookies and Tracks for Internet Explorer

Windows 8 Note  -  PurgeIE, PurgeIE Pro and PurgeFox were designed to work with Microsoft's Internet Explorer. Prior to Windows 8, Internet Explorer utilized files named Index.dat for indexing the Cache, Cookies and History information.

Beginning with Windows 8, Index.dat files are not used. The indexing functions are implemented within a Microsoft database system.  The default structure for the Primary I.E. Folders below is used in Windows 8 except for not containing the Index.dat files.

Each of Internet Explorer's primary folders (directories) - Cache, Cookies and History make use of an indexing technique to maintain information. The index information is contained in files named Index.dat.

For Cookies and for Cache, the Index.dat files are basically URL entries and pointers to the associated real files.  

URL is an acronym for Uniform Resource Locator which is geek for an Internet Address.

For History, no files are referenced (this is the collection of URL entries used for AutoComplete and for controlling the highlighting of imbedded links on the Web pages). All three contain the actual URL plus date/time stamps and reference counts.

Data errors can occur within the Index.dat files and they can get out of sync with the files they reference. Power failures, System failures and improper shutdown procedures can cause the data errors. Data errors can also occur within the actual data files.  Any of these these Index.dat errors are considered to be corrupted cache.  

This has been documented in a separate page -

Reports of systems locking up when one attempts to enter data into the I.E. Address Bar can generally be attributed to errors in the Index.dat file used to record 'Visited URLs'.  This is within the History folder as described below.  

The Default Structure of the Primary I.E. Folders

Cache Folder:

<base>\temporary internet files\content.ie5 [dir]
<base>\temporary internet files\content.ie5\
<base>\temporary internet files\content.ie5\..random1.. [dir]
<base>\temporary internet files\content.ie5\..random1..\..cache files..
                   - - - - - - - - - - - - - -
<base>\temporary internet files\content.ie5\..random8.. [dir]
<base>\temporary internet files\content.ie5\..random8..\..cache files..

Cookie Folder:

<base>\cookies [dir]
<base>\cookies\..cookie files..

History Folder:

<base>\history\history.ie5 [dir]
<base>\history\history.ie5\mshist01.. [dir]
            - - - - - - - -
<base>\history\history.ie5\mshist0n.. [dir]

Notes -

[dir] indicates that the line represents a folder (or directory) name.

The folder levels 'content.ie5' and 'history.ie5' were introduced with IE-5. They are not used in IE-4.

The Index.dat file within the Cache folder is used to contain URL names, date and time stamps, and pointers to the actual cache files which are spread among the four to eight cache sub-folders. These sub-folders are named with randomly-generated 8-character names.

The Index.dat file within the Cookie folder is used to contain URL names, date and time stamps, and pointers to the actual Cookie files which are stored within this same folder.

The Index.dat file within the upper level of the History folder is used to store 'Visited URL' names, date and time stamps. This is the data used by I.E. for its AutoComplete function and controlling the highlighting of imbedded links on the displayed Web pages.

There is one 'mshist...' file for each day of history that you have instructed I.E. to retain. The daily history is stored in the subordinate Index.dat files.

For the above, <base> illustrates the base portion of the path to the folder. This varies widely between the various combinations of Operating Systems and I.E. versions.

For the simplest systems without user profiles, it could be:  "C:\WINDOWS"

For a Win-9x system with profiles, it could be:  "C:\WINDOWS\PROFILES\login-name"

For a Win-2000 system, it could be:  "C:\DOCUMENTS AND SETTINGS\login-name\LOCAL SETTINGS" 

Additional Folders in VISTA IE-7

When User Access Control is enabled for VISTA, the new Protected Mode functions makes use of an additional layer of I.E. Folders.

The choice as to which set of folders to use for a particular website is based on your Internet Security Zone settings.

Using the default set of Internet Security options causes the additional set of I.E. Folders to be used for all Cache, Cookies and History for the Internet Security Zone and the Restricted Security Zone.

The normal I.E. folders in the older structure are used only for the Cache, Cookies and History for the Trusted Security Zone.

Cache Folder for VISTA Protected Mode:

c:\users\login-name\appdata\local\microsoft\windows\temporary internet files\low\content.ie5 [dir]
c:\users\login-name\appdata\local\microsoft\windows\temporary internet files\
c:\users\login-name\appdata\local\microsoft\windows\temporary internet files\low\content.ie5\..random1.. [dir]
c:\users\login-name\appdata\local\microsoft\windows\temporary internet files\
low\content.ie5\..random1..\..cache files..
                   - - - - - - - - - - - - - -
c:\users\login-name\appdata\local\microsoft\windows\temporary internet files\
low\content.ie5\..random8.. [dir]
c:\users\login-name\appdata\local\microsoft\windows\temporary internet files\
low\content.ie5\..random8..\..cache files..

Cookie Folder for VISTA Protected Mode:

c:\users\login-name\appdata\roaming\microsoft\windows\cookies\low [dir]
c:\users\login-name\appdata\roaming\microsoft\windows\cookies\low\..cookie files..

History Folder for VISTA Protected Mode:

c:\users\login-name\appdata\local\microsoft\windows\history\low\history.ie5 [dir]
c:\users\login-name\appdata\local\microsoft\windows\history\low\history.ie5\mshist01.. [dir]
            - - - - - - - -
low\history.ie5\mshist0n.. [dir]

Notes - 

    These folders are not used if User Access Control is not enabled on your system.

    The normal I.E. folders for VISTA would be the same names without the "low" subfolder.

PurgeIE Options vs. Index.Dat Files and I.E. Folders

The PurgeIE Online Cache option and the Offline Cache option process the Cache Folder.  This includes both the Temporary Internet Files and their associated reference entry in the Cache Index.dat file. 

The Offline Cache option works with the entries that were downloaded for "Offline Viewing".   

The Online Cache option works with the remaining entries.

The PurgeIE Unprotected Cookies option processes the Cookie Folder.  This includes both the Cookie data files and their associated reference entry in the Index.dat file within the Cookie folderCookies you have protected with PurgeIEís 'Protect' function will be retained.

The PurgeIE Strays option checks the Index.dat files vs. the referenced data files for both the Cache Folder and the Cookie Folder.  

Cookies and Cache local files that are not indexed by their respective Index.dat files will be deleted.

Conversely, index entries within these Index.dat files that refer to non-existing data files will be deleted.

The PurgeIE Visited URLs option processes the Index.dat file within the upper level of the History Folder.  (This is the record of the Websites you have visited)

The PurgeIE History Folders option processes the daily History files and subfolders within the History Folder

Note - some combinations of Windows Operating Systems and Internet Explorer versions prevent this function from deleting the daily History files.  These combinations keep some of the daily History files open whenever Windows is operating.  Internet Explorer 4.0 running on Win-98 systems exhibits this problem.

PurgeIE does not delete Index.dat files.  PurgeIE does not shrink Index.dat files.  These operations could only be done using DOS mode while Windows is closed.  Competing products that remove Index.dat files require you to reboot your system to perform a cleanup.

PurgeIE cleans the 'Index.dat' files by using approved Microsoft program functions to remove the entries from the 'Index.dat' files.  These API functions reset the URL information to blanks within the Index.dat files which, effectively, eliminates the information that is of greatest concern to  privacy advocates.

PurgeIE does contain an Emergency function for deleting Index.dat files should the need arise.  This would require a reboot.  If you delete Index.dat files, Internet Explorer will create new empty ones at its first opportunity. 

This has been documented in a separate page -

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Revised: August 23, 2015