MUM File – What is .mum file and how to open it?

Definition and Function of MUM Files

A MUM (Microsoft Update Module) file is a Windows update package that contains updates for system files and drivers. It is typically used in conjunction with a CAB (Cabinet) file to deploy updates to multiple computers. MUM files are essential for maintaining the stability and performance of Windows operating systems.

How MUM Files Work

MUM files are structured based on the Microsoft Update Packaging Format (MUP). They contain a set of instructions that specify which system files should be updated, along with the updated versions of those files. When a MUM file is installed, the update process is automated, ensuring that the correct files are replaced without any manual intervention.

MUM files also contain dependency information, which ensures that the required updates are installed before the MUM file can be applied. This dependency mechanism helps prevent update conflicts and ensures a smooth update process. MUM files are typically associated with cumulative updates, which package multiple updates together for efficient deployment.

Opening MUM Files on Windows

MUM files, short for Microsoft Update Metadata, are essential components of Windows Vista and later operating systems, containing critical metadata and installation instructions for system updates. To open a MUM file, certain conditions must be met:

• Elevated Permissions: As MUM files are system-critical, they require elevated permissions to access and modify. Right-click the MUM file, select “Properties,” and navigate to the “Security” tab. Grant your user account full control permissions by clicking “Edit” and assigning appropriate permissions.

• DISM Utility: MUM files are primarily managed through the Deployment Image Servicing and Management (DISM) utility. Open an elevated Command Prompt or PowerShell window and type the following command, replacing “pathtomum_file” with the actual file location:


dism /online /add-package /packagepath:path_to_mum_file


DISM will integrate the update package into the system, making its contents available for installation. Note that DISM requires an active internet connection for certain updates.

Once the MUM file is successfully processed, the associated updates will be applied automatically through the normal Windows Update mechanisms. Alternatively, you can manually check for and install the updates via the Windows Update settings.

MUM File Overview

A MUM file, short for Microsoft Update Metadata, is a crucial component of the Windows Update system introduced with Windows Vista. These files contain essential metadata about available updates, including information on the update’s purpose, compatibility, and dependencies. When you initiate the Windows Update process, the MUM files are downloaded and used by the operating system to determine which updates are applicable and necessary for your system.

Role in Windows Update

MUM files play a key role in the efficient and reliable operation of Windows Update. They provide the necessary information to identify and select the appropriate updates for your system, ensuring that you receive the most up-to-date and compatible software. Without MUM files, Windows Update would not be able to accurately determine which updates are applicable, potentially leading to installation errors or conflicts. Additionally, MUM files facilitate the rollback of updates if necessary, ensuring a seamless restoration of your system to its previous state should an update cause any issues.

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