BAK File

What are BAK files and how to open them

Are you having problems opening a BAK file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BAK files.

What is a BAK file?

BAK files have multiple uses, and Backup is one of them. Read more about the other uses further down the page.

Backup File

The .bak file extension is used for general backup files. Many applications and computer processes use the .bak extension to create backups of documents that the program is creating.

The .bak file extension is a common file extension for the files created by the auto-save features found in many computer applications. For example, when you are editing a document in Microsoft Word and the auto-save feature kicks in, a .bak file will be created.

Files with the .bak extension are also commonly created before your computer begins to execute a complex operation, ensuring your data will be restored if something happens during the process.

These files are typically automatically deleted by the application that created them when the file is no longer needed or left behind so you have a copy of your data that can be manually restored if required.

How to open BAK files

We have identified one BAK opener that is compatible with this specific type of BAK file.

Programs that open Backup files

Last updated: August 23, 2026

All known file formats using extension .BAK

While Backup File is a popular type of BAK-file, we know of 3 different uses of the .BAK file extension. Different software may use files with the same extension for different types of data.

Microsoft SQL Server Backup File

Microsoft SQL Server Backup File stores the full or partial copy of a SQL Server database or transaction log so that it can be restored later. It is created by the SQL Server database engine (via T-SQL BACKUP statements) as a single file on disk or other backup media. It contains database pages, log records, header metadata, and optional features like compression or encryption.

Creation involves issuing a BACKUP command (for example, BACKUP DATABASE or BACKUP LOG) which writes data to a disk file. SQL Server can store one or more "backup sets" in the same file if backups are appended. To inspect what's inside, SQL Server provides commands like RESTORE HEADERONLY (shows metadata about each backup set), RESTORE FILELISTONLY (lists data and log files included), and RESTORE LABELONLY (information about the backup media).

Backup files may be compressed or encrypted depending on SQL Server version and options used. The header metadata includes items like the database name, server name, backup type (full, differential, log, file, etc.), start and finish times, version number, and flags for compression. SQL Server also records logical and physical file names inside the backup so that restore operations know which files to create or move.

A technical identifier appears near the very start of the file: at offset 0 there is an ASCII signature "TAPE" followed by binary bytes, and at offset 93 there is Unicode text "Microsoft SQL Server." Other identifying strings in the content include object labels such as UNIQUEIDENTIFIER, COLLATION, TIMESTAMP, FILENAME, BACKUP, VERSION, COLUMN, etc.

While we have not verified the apps ourselves yet, our users have suggested ten different BAK openers which you will find listed below.

MIUI Backup Data

MIUI Backup Data files are used by the MIUI operating system on Xiaomi devices to store local backups of apps, system settings, media, and user data. These backups are made via the built-in MIUI "Local Backups" feature and saved in a folder such as MIUI/Backup/AllBackup on the device storage. These files serve to restore the device to a previous state in case of system changes, resets, or to migrate data between devices.

A backup operation produces multiple files: one or more .BAK files that hold data for individual apps or system components, plus a descript or description XML file (often named descript.xml) that lists metadata for each .BAK file such as package name, app display name, backup type, file size, and state. During restoration, MIUI uses the XML file to know which .BAK files correspond to which apps or data. Sometimes moving or renaming these files improperly causes restore failures.

Every .BAK file from MIUI Backup Data begins with the ASCII signature "MIUIBACKUP" at offset 0, followed by a newline and an additional header which includes app package name, app display name in UTF-8, version identifiers, and other lines before the core data. The backup then wraps a standard Android backup ("ANDROID BACKUP" header), so after skipping MIUI's extra header block (roughly five lines), tools designed for Android's standard backup format can process the rest.

Various apps that use files with this extension

These apps are known to open certain types of BAK files. Remember, different programs may use BAK files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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