A DAT file is a generic container that holds data your programs create, but you usually don't need to open it yourself

A DAT file is a catch-all format that software uses to store information it needs to run. Unlike a Word document or a photo, a DAT file has no standard structure — the program that created it is the only one that knows what's inside. Your computer may have dozens of DAT files scattered across folders, most of them working silently in the background.

The name "DAT" tells you almost nothing about what the file contains. One DAT file might hold email settings. Another might contain game progress. A third might be a temporary cache your web browser created. Because DAT is so generic, Windows and Mac don't know what to do with them if you try to open one directly — they'll ask you which program should handle it, and if you pick the wrong one, you'll see gibberish.

Most DAT files are not meant for you to touch. They exist so your programs can remember things between sessions. You back them up the same way you back up everything else: by including the folder they live in when you copy your files to an external drive or cloud storage.

Key Takeaways

  • DAT files are data containers created by software to store settings, caches, or other information the program needs to function.
  • You should not try to open a DAT file unless you know exactly which program created it, because opening it in the wrong process will show only unreadable text.
  • Most DAT files are temporary or system files that work in the background and do not need your attention.
  • When backing up your computer, DAT files are included automatically if you back up the entire folder where they sit.

Where DAT files come from and what they do

Programs create DAT files to store information they need to remember. Microsoft Outlook uses DAT files to cache your email. Steam (the video game platform) creates DAT files to track your game library and settings. Your web browser may create DAT files as temporary storage while you browse. Windows itself creates DAT files in system folders to log events and store configuration data.

The reason software uses DAT as a format is straightforward: it's a label that means "this is data, but you don't need to know the structure." The program that created the file knows how to read it. Your operating system does not, and neither do you. This is by design — these files are not meant to be edited by hand.

Some DAT files are temporary and disappear when you close the program or restart your computer. Others are permanent and accumulate over time. A corrupted DAT file usually just means that program loses some settings or cached information the next time it runs — it's rarely a serious problem.

When you might see a DAT file and what to do about it

You'll most often encounter DAT files when you're organizing backups or cleaning up your hard drive. You might see them in your Downloads folder (left behind by an installer), in your AppData folder (where Windows stores program settings), or in a game folder (where the game stores your progress). You might also see them if you're looking at the contents of an external drive or cloud backup.

In most cases, you should leave DAT files alone. Do not delete them unless you're sure you don't need the program that created them, because deleting a DAT file can cause that program to lose settings or data. Do not try to open one by double-clicking it — Windows will ask you which program to use, and guessing wrong will not harm anything, but you'll just see unreadable characters.

If you need to know what a specific DAT file contains, search the filename online along with the program name. For example, searching "Outlook.ost" will tell you it's Outlook's offline storage file. Searching "nvapps.bin" will tell you it's an NVIDIA graphics driver cache. Once you know what it is, you can decide whether to keep it.

DAT files and your backup strategy

When you back up your computer, DAT files are included automatically if you're backing up entire folders or using a full-system backup tool. You don't need to do anything special to preserve them. If you're using cloud storage like OneDrive or Google Drive, DAT files in your Documents or Desktop folders will sync just like any other file.

The only time DAT files matter for backup is if a program depends on them to restore your settings. For example, if you back up your Outlook data folder (which contains DAT files), you can restore your email and calendar to a new computer. If you back up your game folder, you can restore your game progress. This happens automatically — you don't need to identify or handle the DAT files separately.

If you're trying to reduce the size of a backup, some DAT files are safe to exclude. Temporary cache files (often labeled with "cache" or "temp" in the filename) can usually be deleted without harm — the program will recreate them. But if you're unsure whether a DAT file is temporary or essential, it's safer to include it.

Common DAT files you might encounter

Some DAT files appear on almost every Windows computer. The file thumbs.db is a cache of thumbnail images Windows creates in folders with many pictures — it's safe to delete, and Windows will recreate it. The file desktop.ini stores folder display settings and is safe to leave alone. Files named nvapps.bin or similar are graphics driver caches and can be deleted if you need space, though they'll be recreated.

In program folders, you might see DAT files with names like config.dat (program settings), cache.dat (temporary data), or data.dat (program information). On Mac, you might see .dat files in the Library folder, which serve similar purposes. None of these require your attention unless the program stops working properly.

Email programs create some of the most important DAT files. Outlook creates .ost files (offline storage) and .pst files (personal storage) that hold your actual email and calendar data. If you're migrating email to a new computer, these are the files you need to preserve. Other email clients like Thunderbird create similar files with different extensions.

How to tell if a DAT file is causing a problem

A corrupted or missing DAT file rarely causes a serious crash. More often, you'll notice that a program has lost some information — your game progress is gone, your browser forgot your passwords, or your email client can't find your messages. If this happens, the first step is to restart the program or your computer, because sometimes a DAT file just needs to be rewritten.

If restarting doesn't fix it, you can try deleting the DAT file and letting the program recreate it. This will reset that program's settings to defaults, but it usually solves the problem. To do this safely, close the program completely, find the DAT file in Windows File Explorer or Mac Finder, and move it to the Trash instead of permanently deleting it. Then restart the program. If the problem persists, you can restore the original file from your backup.

For important programs like email or games, this is another reason to keep regular backups. If a DAT file becomes corrupted and you can't recover it, you can restore the entire folder from your backup and pick up where you left off.

Frequently Asked Questions

Is it safe to delete a DAT file?

It depends on the file. Temporary cache files (often labeled "cache" or "temp") are safe to delete — the program will recreate them. System or settings files should be left alone unless you're sure the program is no longer installed. When in doubt, move the file to the Trash instead of permanently deleting it, so you can restore it if something breaks.

Why can't I open a DAT file?

Because DAT is a generic format with no standard structure, your operating system doesn't know how to read it. Only the program that created the file knows its internal format. You can try opening it with a text editor to see if it contains readable text, but most DAT files will show only gibberish because they're stored in a binary format.

Do I need to back up DAT files separately?

No. If you're backing up the entire folder where a DAT file sits, it's included automatically. You don't need to identify or handle DAT files separately — just back up the program folder or the system folder where they live, and they'll be preserved along with everything else.

What's the difference between a DAT file and other file types?

A DAT file has no specific format — it's just a label meaning "data." A JPEG is always a photo, a DOCX is always a Word document, but a DAT file could contain anything. This is why you can't open a DAT file without knowing which program created it, whereas you can open a JPEG with any image viewer.

Should I exclude DAT files from my backup to save space?

Only if you're certain they're temporary cache files. Temporary files are safe to exclude and will be recreated by the program. But if you exclude settings or data files, you'll lose program configuration or important information if you need to restore your computer. When in doubt, include them — the space they take is usually small compared to photos and documents.