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I have a hidden file called MSO Cache on my E drive. Windows XP is installed on the C drive. Msocache is about 200 megabytes but it looks kind of important. I'm sure I didn't make it nor anybody else. Is it a system file or spyware? What does it do and can I delete it safely?

Msocache is another of those "magical" directories (not a file) that somehow just appears one day. Since we're not looking for this kind of thing constantly it's easy to miss exactly when it showed up.

Here's one clue, though - MSO stands for MicroSoft Office.

Yep. Microsoft Office is trying to be helpful.

First, Microsoft does have a Knowledgebase article on this, though the title's not particularly helpful: Local Install Source (Msocache).

The bottom line is that it's simple a local copy of Microsoft Office's installation source. Put another way, it's a copy of portions of the Microsoft Office installation CD. Why? so that you don't have to insert the CD when you add a feature, perform a repair operation, or install service packs and patches.

Msocache is created, quoting the KB article:

...if the following conditions are true:

  • One of the available hard drives has more than 1.5 gigabytes (GB) of free disk space available.
  • The hard disk with sufficient space is not a removable drive or a network drive.

Personally that seems kind of arbitrary, but there ya go.

You can delete the folder, but, that same Knowledgebase article goes on to say, "Never delete the MSOCACHE folder by using Microsoft Windows Explorer." Why, I do not know. They suggest using the Windows Disk Cleanup Wizard.

Article C2461 - November 17, 2005 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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17 Comments
Bubba
November 18, 2005 2:04 PM

" 'Never delete the MSOCACHE folder by using Microsoft Windows Explorer.' Why, I do not know."

Because you will hurt MicroSoft Office's feelings.

Bill
December 20, 2005 4:20 PM

I have used diskcleanup to get rid of MSOCache but it still remains. The dirs are actually on my H: drive. My other problem is all my attempts to update MS Office 2003 fail.

Tod
May 13, 2006 10:37 AM

I can't even get windows diskcleanup to get rid of it as it wont recognise its existance. Bets left alone, dont want to upset it ;)
Tod
www.linkup-media.com

Avner Falk
June 17, 2006 3:02 PM

P.S. After all the above, manually delete your MSOCache folder in your Windows Explorer (despite Microsoft's warning), then rerun your Registry Cleaner, which will find a few dozen new invalid entries in your Windows Registry. Delete those, and your problem is solved (hopefully ...)

painterr
September 1, 2006 2:58 PM

I use a little program called unlocker that is a freeware I got off the internet and deleted it with no problem!

Mark Plant
May 21, 2007 4:48 AM

The reason you should not just delete this file with windoze exploder is that it has registry entries pointing at it that will remain behind after the delete, and will bite you later.

WeyrleaderZor
September 24, 2007 12:04 PM

You can use this tool (see direct-to-download URL below) from Microsoft to cut back on what is in the MSOCache directory, or to remove all Local Install files period. Very handy - why it needs to be done with this (or assumably a DOS prompt when Windows wasn't booted (ie: A boot disk or recovery/repair console) I don't know... But this IS the "official" way to "uninstall" the MSOCache files.

http://download.microsoft.com/download/b/7/b/b7b7d0e1-f125-46ed-9d65-95350e8d3f96/LISTool.exe

none
December 28, 2007 10:14 AM

the uninstall tool does not work for office2007 there is no mso.dll

Matt
September 29, 2008 1:02 PM

Why keep the files if you have them? Windows update may/will fail with Office updates, probably other tools as well, if you delete the files without cleaning up the registry. I'm currently in that situtation. Even changing drive letters can affect if the auto-update finds the installation as being not intact; move your CD/DVD to drive Z:. It tries to open files where it thinks they should be and may conclude that the installation is corrupted and stop. In my case, I removed the default Acer laptop D: partition, single drive with two partitions, after I installed Office. Windows update will no longer auto-update Office. It fails for all updates. No going back in my case. Now I'm trying to find the correct registry entires to remove or blank contents to avoid this check from failing the update.

John Lee
October 17, 2008 9:16 AM

Today, out of the blue, one big carpet "magically" move it self from the root directory, to the MSOCache carpet.
Yestarday, Windows made an atomatic update.
Could this be the reason?
Anyone?

I'm afraid I don't know what you mean by 'carpet'.
- Leo
18-Oct-2008

Roy Basan
January 3, 2009 3:05 AM

How about transferring the MSO Cache from the C to the D drive would it be better than deleting it.
I am planning the transfer the contents of the folder in that drive and is looking for comments from knowledgeable people. Looking forward to your valuable suggestions
Thanks!

p
January 7, 2009 9:38 AM

You can just delete MSOCache folder if you have the installation CD around. The LISTool.exe just enables selectively deleting stuff from MSOCache folder.

Marilyn Moroni
March 4, 2009 6:44 AM

I lost my Graphics file and when I went looking for it I found it in a MSOcache file.
How could that happen.Ciao, Marilyn

Richard FDisk
April 30, 2009 6:49 PM

MSOCache is annoying @ best especially when it installs / appears on a disk that's not C:\ (which is where it should be, on C:\);
I don't know the method they programmed office to search for available space but it would seem to be that it checks from the CD Drive letter and then goes down one at a time rather than first checking C:\ which is what it should do (bad programming I guess, Oh yeah, it's MS)
the next time I install I'll try removing all the drive letters except the CD / DVD drive and C:\
- - - ->
you can move the Office 2003 MSOCache from any drive to any drive using any method of file transfer (windows exploder, command window, etc.), just do a registry edit to search for MSOCache and change the drive letter indicated in each entry to the new location doing it from an administrator account = success

Leon
July 22, 2009 8:50 AM

You said MSO cache is about 200 MB; mine is 3.5 GB!

Vincent
December 30, 2010 3:43 PM

Welllll..............

i thought i would just drop to dos and erase my unneeded msocache folder hahaha

i typed "erase c:\msocache\*.* /s /f /q"

i am now reinstalling windows!!!!

Troy
September 16, 2012 6:54 AM

I know you posted this article 7 years ago which seems like an eternity in the tech world but it still is timley. The MSOCACHE is still an issue. I wanted to add: The reason they ask you NOT to delete using Windows Explorer is because of all the path statemtents pointing to resources in the MSOCACHE. If you use the cleanup tool it will remove the pointers so that MS Office doesn't try to use those resources when you add a feature to office, instead it will prompt you for the CD. And there you have it :-)

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