What are the $NtUnstallKB* folders in my Windows folder, and can I delete them?.

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Summary: Windows Updates saves uninstall information into hidden folders that, with a little planning, can be deleted to free up disk space.

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Your guess is exactly right.

Let's look at what you're looking at, and I'll describe the safe approach to dealing with this.

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If you open Windows Explorer on your Windows Directory (typically C:\Windows), you may see the folders mentioned in our question:

(You will need to have "View hidden files and folders" enabled in Windows Explorer's options to be able to see these folders.)

They're colored in Blue because the files within the folders are compressed to save space.

The names indicate what they are: uninstall information for various patches and updates. Most are named including a "KB number" which is the Microsoft Knowledgebase number that describes the patch that they are related to.

Yes, except for $hf_mig$, you can delete them. ($hf_mig$ is apparently used for coordination by future patches.) As you mention, the "cost" is that you will no longer be able to uninstall the corresponding patch. For most of us that's not really a big deal. In fact, just quite coincidently, I did exactly this earlier today on one of my machines that was running low on disk space on it's C: drive.

However, as you might expect, sometimes just blindly deleting things doesn't always end up with what you might expect. Sometimes we make mistakes, and sometimes down the road we might wish we hadn't deleted them.

Two suggestions for you:

• Take a full system backup that you plan to keep prior to deleting the folders. In particular, this can save your bacon should you happen to accidentally delete something you didn't intend to. Keep the backup image so that should you ever need these folders and files again you can recover them from the backup.

• Copy these folders to somewhere else manually first. Perhaps copy them to another system, or another disk with more room, or burn them to a CD or DVD. Once again the goal here is to feel confident that should you need to replace the folders and files, you can because you kept a copy.

In general, I actually advise that you leave these folders alone unless you have a reason to remove them. They don't impact system performance, and the ability to uninstall a patch has come in handy for some folks from time to time. If you find that you're running low on disk space on the drive housing Windows, then yes, these are on the list of things to consider removing.

Removing safely by copying them elsewhere first, that is.

Related:

• Can I delete these randomly named folders? Folders with random and unreadable names will occasionally appear on your machine. They're typically the side effect of an update that didn't clean up.

• Is it safe to delete this file? Looking for large files when running out of disk space makes sense. We look at the steps to determine whether a file, such as a .data file, is important.

• Where's my disk space going? It's not uncommon to run out of disk space. A free utility can help tell where's your disk space is going so you can determine what steps to take.

Article C3458 - July 26, 2008

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