I don’t know.
Honestly, I have no idea either what they are, how they got there, or why they occupy so much space. That’s the problem with “.dat” files — there’s no way to know what they are without more information.
But I do have some ideas on how to determine if deleting them is ok, and ways to do it safely — and those ideas apply to any file type, not just “.dat”.
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First, I need to reiterate: there’s no way to know what a “.dat” file is without knowing what program created it. The file extension “.dat” is a generic extension, often used to represent nothing more specific than “data”. As a result, it is used by many, many applications. There’s no way to know what the file contains, or what to do with it, without first knowing which application created it.
So, how do you determine if a file — any file — matters?
Well, my first suggestion is the most important one.
Back up first
Before you do anything, back up the files. Copy them to thumbdrives, copy them to another computer, take an image backup of your machine, if you like, just do something, anything, so if you discover that you really did need that file after all, you can get it back.
You may find the file is an important part of some application you rely on daily; or worse, an application you only use once a month or so. If you simply delete the file, it’s gone without reasonable hope of recovery. If you’ve backed it up somehow, you’ll not only be able to remove it from your system, you’ll be able to put it back if you discover removing it was a mistake.
My next steps are fairly simple.
First, rename the file or files. Use your computer for a while. Reboot. If an error occurs related to the missing original file name, you now know what the file was about, and can decide what to do based on the error you get. If you discover no errors, you’re ready to move to the next step.
Next, delete file or files. (You did back them up, right? Right?) Same exercise. Use your computer for a while. Reboot. Use it for different things to exercise some of the applications you have on the machine. Once again, if an error occurs related to the now missing file, you now know what the file was about, and can decide appropriately based on the error you get. If you discover no errors, you’re done. Sort of.
Last, remember that you deleted the file and where you put the backup. Our simple tests above may not actually have fired up the application or scenario that required the file. You may not find out until some lengthy time down the road that … whoops! … the file you deleted some months ago turned out to be part of an application you haven’t touched in ages. Hence, again, the importance of the backup.
If you can’t delete
If you can’t delete or rename the file, it’s possible that’s because the file is in use.
That’s great! It tells you that the file matters. If you like, you can then use a tool such as Process Explorer to figure out what program’s using it. Once you figure that out, you can once again decide the right course of action based on knowing which application is accessing the file.