MSR Partition in Windows: Everything You Need to Know and How to Manage It

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When we manage disks in Windows and we come across the mysterious Microsoft Reserved Partition, better known as MSR, it's normal to wonder what it's for, if it's really important, and if we can safely delete or modify it. If this term sounds familiar because you're installing Windows or configuring new disks, this article is designed to answer all those questions, explaining in detail its function, how it's created, what happens if it disappears, and how to act in each situation. Below, you'll find a complete, clear, and thoroughly updated guide on the MSR partition in Windows.

Before you rush into your partitions or panic over the error messages that often appear when managing GPT and MBR disks, it's important to understand the actual purpose of the MSR partition, the risks involved in deleting it, and why, in most cases, you should leave it alone. Learn everything you need to know about this essential part of your system, along with practical tips and how to act if an accident forces you to restore it, always with a safe and simple approach.

What is MSR partition in Windows?

La MSR partition (Microsoft Reserved Partition) is a small space that Windows reserves on hard drives that use the GPT (GUID Partition Table) partition scheme. Its main function is to save space for internal operating system tasks, not storing user-accessible data or essential boot files (those go on the EFI partition). This partition, although usually invisible to the user, is key for partition management and to allow future expansions or changes to the disk without having to completely reorganize it.

In simple terms, the MSR partition acts as a "save space" for future system needs, ensuring that Windows can operate and reorganize partitions efficiently if necessary. It typically has between 16MB and 128MB in size, depending on the disk capacity:

• On GPT disks smaller than 16 GB: MSR takes up 32 MB.
• On GPT disks larger than 16 GB: MSR takes up 128 MB.

When you initialize a new disk in GPT format and install Windows, the installer automatically creates the MSR partition, right after the EFI partition (which is responsible for storing the UEFI boot files). If the disk is only used for storage, the first visible partition will be the MSR partition, since the EFI partition is not created in that case.

What is the MSR partition used for?

The main function of the MSR partition is reserve space for system operations, especially related to advanced partition management and internal data structures. Although it doesn't store specific files or is accessible through Windows Explorer, it's essential for:

• Allow the creation of future protected or system-reserved partitions.
• Avoid space conflicts when creating or modifying partitions with Windows tools.
• Facilitate expansions or changes to disk layout without having to delete and recreate other partitions.

While the MSR partition does not house user data or critical startup files, It is essential for the disk to function optimally under WindowsThe operating system manages this space as it pleases, and since it is hidden and unformatted, the user cannot use it directly, nor is it possible (or advisable) to assign it a drive letter.

What is the difference between MSR and EFI partition?

On disks under the GPT scheme, in addition to the MSR, there is usually also a partition EFI (Extensible Firmware Interface). The two are often confused, but it's important to be clear about the following:

• The EFI partition stores the UEFI firmware and boot files, necessary to start the operating system.
• The MSR partition simply reserves space for future system operations, without saving any important files or being necessary to boot Windows.

In short, if the EFI partition is deleted or corrupted, Windows won't boot. Losing the MSR partition can cause partition management issues and sometimes prevent Windows from being reinstalled or upgraded, but it doesn't always prevent immediate booting.

When and how is the MSR partition created?

Windows automatically creates the MSR partition during installation on a GPT disk. If you connect a secondary GPT disk to your computer and it doesn't already have an MSR partition, It can be created automatically when initialized with disk management or DiskPart. You don't need to create it manually in most cases.

Only when you are doing an advanced custom installation or unattended deployment of Windows, you might need create it yourself using tools like DiskPart or specific XML commands for automatic configurations. However, this is rare, and creating one manually is not recommended unless explicitly suggested in official Microsoft documentation.

How to create an MSR partition manually

If you're sure you need an MSR partition on a new GPT disk and you're going to create it manually, you can do so by following these steps from the command prompt (cmd) as an administrator:

• Open the Start menu and search for "cmd." Right-click and select "Run as administrator."
• Write diskpart and press Enter to open the DiskPart utility.
• Select the appropriate disk with the command select disk n (where n is the number of your disk).
• To create the MSR partition, run: create partition msr size=128 (size may vary depending on the disc).

Remember that this process will destroy any previous data if you don't select the disk correctly, so be extremely careful and make backups before proceeding. If in doubt, it's best to let Windows manage the MSR automatically.

Can the MSR partition be deleted?

In technical terms, Yes, it is possible to delete the Microsoft Reserved Partition. (for example, by using advanced disk management tools). However, It is NOT ADVISABLE at all to do so., as this can cause partition management errors and even make future system installations or updates impossible. In some cases, errors may occur during the boot process if other dependent partitions are affected.

If you need to free up space and are considering removing the MSR, you should know that its size is very small (maximum 128 MB on modern disks), so the risk does not compensate for the minimal benefit. In case you accidentally delete the MSR partition and your system is still working, make sure that no problems arise when modifying partitions in the future.

What to do if you delete the MSR partition by mistake

Accidentally deleting the MSR partition can, in some scenarios, cause boot errors and the inability to add, move, or extend other partitions. If after deleting the MSR you find that the system won't boot properly, you can try one of the following:

• Restore MSR using third-party tools specialized in partition recovery (for example, solutions like Tenorshare 4DDiG or Wondershare Recoverit).
• Reinstall Windows so that the installer automatically creates the necessary partitions (including MSR and EFI).
• Try creating the MSR manually from a recovery environment using DiskPart, although this may not be sufficient if other critical files are missing.

There are utilities such as Wondershare Recovery y Tenorshare 4DDiG which allow you to analyze the disk in a few steps, in an assisted manner, find deleted partitions and try to restore them:

• Download and install the specialized tool.
• Select the system disk and run the scan.
• Check which files and partitions can be recovered.
• Restore what is necessary and check if the system boots again.

If recovery is not possible this way, the safest method is to reinstall Windows, making sure to create the partition table from scratch in GPT format so that the system itself creates all the required partitions.

How to move MSR partition to another hard drive?

Moving the MSR partition isn't a common or easy practice, but there are situations where it might be necessary (for example, if you mount a second disk or change the primary system disk). To do this, it's recommended:

• Use the Windows Disk Manager to create a new MSR partition on the new disk.
• Copy the necessary data (normally there is no visible content in MSR, but there is in the EFI partition if you also want to move the boot).
• Remove the drive letter from the new MSR, if you had assigned it to make it visible.
• Test booting the system from the target disk, and if everything works, delete the old MSR.
• In case of boot failure, repair the startup with Windows installation media.

Please note that in many cases, cloning the entire disk is preferable if you are replacing the primary system, as manually managing reserved partitions can cause difficult-to-fix errors.

Differences between MBR and GPT disks in relation to the MSR partition

La MSR partition only exists on GPT disksOn traditional MBR disks, Windows creates only the System Reserved partition, which acts as a functional equivalent in that environment. If you try to create an MBR on an MBR disk, you'll receive error messages indicating that it's not supported.

GPT disks:

• They include EFI partition (if it is for the system) followed by the MSR.
• They allow more primary partitions (up to 128) and much larger disk sizes.
• Require UEFI boot mode enabled.

MBR disks:

• Does not include MSR or EFI (except in special configurations).
• Limited to 4 primary partitions (or 3 primary + 1 extended).
• Traditional boot (Legacy BIOS).

If your computer throws up errors when trying to create MSR or EFI partitions on an MBR disk, the solution is to convert that disk to GPT, for which there are tools such as AOMEI Partition Assistant which allows conversion without data loss. It's crucial to check that your system supports UEFI boot before making the switch.

Advanced Configuration: Create MSR Partitions Using Scripts and XML

In professional environments or automated Windows deployments, creating the MSR partition can be done through scripting, using the DiskPart command, or XML configurations for unattended installations. The command would be:

create partition msr size=n

where n is the size in MB.

Multiple partitions, including the MSR, EFI, Recovery, and the main Windows partition, can also be defined using XML blocks so that they appear in the exact order and size desired during the installation process. This is useful for corporate computers or mass installations.

Some important parameters when using DiskPart:

• size=n: partition size in MB.
• offset=n: offset in KB where the partition will start.
• noerr: ignores errors and continues processing the script.

Common Error: "MSR and EFI partitions are only supported on GPT disks"

If you get the error message that says MSR and EFI partitions are only supported on GPT disks, you're most likely trying to create these partitions on an MBR-formatted disk. Remember, these partitions are only valid on GPT disks, so you'll need to convert the disk if you need to use these features.

To convert an MBR disk to GPT without losing data:

1. Back up all important content.
2. Use tools like AOMEI Partition Assistant to convert the disk without formatting.
3. Please confirm that your motherboard supports UEFI mode before starting the conversion.

Frequently Asked Questions about MSR Partitioning

Does the MSR partition store important data?

No, the MSR does not contain essential files or user documents.Its purpose is to reserve space for future system operations. If you try to access it from File Explorer, it won't be visible or usable.

What happens if I delete the MSR?

In most cases, Windows will still be able to boot (unlike the EFI partition), but You may experience serious problems when trying to modify partitions or reinstall the operating system.. Better not touch it.

Can I change the size of the MSR?

It is not recommended to alter its sizeThe benefit of changing this is minimal and can cause internal Windows errors. Let the system manage the size based on the disk.

Is an MSR partition always created on GPT disks?

Virtually always, unless the disk is used exclusively for storage and has never been initialized by Windows or equivalent tools. On disks intended for the system, Windows creates it automatically.