Optimize fails at cookies index.dat

  • 3 September 2020
  • 2 replies

Userlevel 2
Badge +5

I recently discovered that optimization stops before the scan is completed and always stops at the same place.  I also found that the file on which it stops does not exist.  I am not sure whether the scan is actually completed and just does not reflect that in the progression or, the optimization actually stops before it is completed.  How can I tell and if it is the latter, how do I fix it?  I have removed and reloaded the program 4 times and this continues to happen.  The is a relatively new event that I discovered about a month ago.

I would appreciate any help / insight. 

Thanks much.



Best answer by Joseph1973 11 September 2020, 03:33

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Userlevel 7
Badge +63

Hello @Joseph1973 


Make sure Internet Explorer is not running what you optimize and see if it completes? Even check with Task Manager and if it’s running kill the processes then try System Optimizer.


“In the Microsoft Windows operating system, index.dat is a database file used by the Internet Explorer web browser. It is used to improve performance.”




The index.dat file is a database file. It is a repository of information such as web URLs, search queries and recently opened files. Its purpose is to enable quick access to data used by Internet Explorer. For example, every web address visited is stored in the index.dat file, allowing Internet Explorer to quickly find Autocomplete matches as the user types a web address. The index.dat file is user-specific and is open as long a user is logged on in Windows. Separate index.dat files exist for the Internet Explorer history, cache, and cookies.


The index.dat file is never resized or deleted. A large index.dat file can impair performance.


Note: The .dat extension is commonly used for data files (files that are not human-readable and do not hold a document-based binary file). It's possible to find files named 'index.dat' that are not used by Internet Explorer.”



Userlevel 2
Badge +5

TripleHelix ! Hello ! 

The answer to this issue actually turned out to be more complicated than I had anticipated.  In the end, however, there were three selections in the optimization menu that I had to unselect in order for the optimization cycle to complete. 

The first was……..  the  Clean Index.dat (cleaned on reboot).  This resolved the initial issue regarding the index.dat file that does not actually exist, or at least not on my machine.  Unfortunately, another item began to stop the optimization…….  “software\microsoft\Protected Storage System Provider”.  I did not have a clue.

I checked it out, however, and discovered  this was related to Outlook, and being that I had nothing like this in my system registry, I also unselected………  Internet Explorer - URL History   and    Microsoft Office - Recent File and Folder List.    I was able to confirm these through process of elimination and all is working fine again.