Microsoft Reserved Partition
msftres flagA Microsoft Reserved Partition (MSR) is a partition of a data storage device that uses the GUID Partition Table (GPT) layout. The Windows operating system uses this partition for compatibility purposes. No meaningful data is stored within the MSR. Rather, when compatibility needs arise, Windows shrinks this partition to make way for other special-purpose partitions, which may contain data.[1] The GPT label for this partition type is E3C9E316-0B5C-4DB8-817D-F92DF00215AE.[2]
Purpose
[edit]Formerly, on disks formatted using the master boot record (MBR) partition layout, certain software components used hidden sectors of the disk for data storage purposes. For example, on dynamic disks, the Logical Disk Manager (LDM) stores metadata in a 1 MB area at the end of the disk which is not allocated to any partition.[3]
The UEFI specification does not allow hidden sectors on GPT-formatted disks. Microsoft reserves a chunk of disk space using this MSR partition type to provide an alternative data storage space for such software components which previously may have used hidden sectors on MBR-formatted disks. Small, special-purpose partitions can be allocated from a portion of the space reserved in the MSR partition.[1]
Specifications
[edit]The MSR should be located after the EFI System Partition (ESP) and any OEM service partitions, but it must be located before Windows partition.[1] Microsoft expects an MSR to be present on every GPT disk, and recommends it to be created as the disk is initially partitioned.[4]
The GPT label for this partition type is E3C9E316-0B5C-4DB8-817D-F92DF00215AE.[2]
The Microsoft-recommended size of MSR (which Windows Setup uses by default) is different for each version of Windows:
| Windows version | MSR's size |
|---|---|
| Windows 7 | 128 MB[4] |
| Windows 8 & 8.1 | 128 MB[5] |
| Windows 10 & 11 | 16 MB[6][7] |
See also
[edit]- Basic data partition (BDP)
- EFI System Partition (ESP)
References
[edit]- 1 2 3 "Windows and GPT FAQ". Windows Hardware Developer. Microsoft. 16 Jul 2024 – via Microsoft Learn.
- 1 2 "PARTITION_INFORMATION_GPT structure (winioctl.h)". Windows App Development. Microsoft. 24 Feb 2024 – via Microsoft Learn.
- ↑ "How Dynamic Disks and Volumes Work". Windows Server 2003 Technical Reference. Microsoft. 8 October 2009 – via Microsoft Developer Network's Archive.
- 1 2 "Recommended UEFI-Based Disk-Partition Configurations". Windows 7 Technical Library. Microsoft. 30 October 2012 – via Microsoft Learn's archive.
- ↑ "Configure UEFI/GPT-Based Hard Drive Partitions". Windows 8.1 and Windows 8 Technical Library. Microsoft. 10 December 2014 – via Microsoft Learn's archive.
- ↑ "UEFI/GPT-based hard drive partitions (Windows 10)". Windows Hardware Developer. Microsoft. 10 February 2023 – via Microsoft Learn.
- ↑ "UEFI/GPT-based hard drive partitions (Windows 11)". Windows Hardware Developer. Microsoft. 2 October 2023. Retrieved 2 May 2025 – via Microsoft Learn.
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