Microsoft Reserved Partition
The Microsoft Reserved Partition, or MSR, is a partition on a data storage device that is labelled with Globally Unique Identifier (GUID) equal to E3C9E316-0B5C-4DB8-817D-F92DF00215AE. The containing storage device has to use the new GUID Partition Table (GPT) format, not the traditional master boot record (MBR) partition table format.
GPT disks do not allow hidden sectors. MSR is used to reserve space ahead of time for software components which will later allocate space by reducing the size of the MSR and creating a component specific partition. For example the conversion of a basic disk to a dynamic disk requires space for holding the dynamic disk database.
MSR does not contain any meaningful data itself.
Microsoft requires an MSR on every GPT disk, and recommends it to be created as the disk is initially partitioned. It should be located after the EFI System Partition (ESP) and any OEM service partitions, but it must be located before any primary partitions of bootable windows operating systems. Initial size of MSR is 32 MB on disks smaller than 16 GB, or 128 MiB (134,217,728 bytes) on other disks.
The MSR partition is not visible within Microsoft Windows Disk Management GUI-control utility but it is listed with Microsoft command line utility (diskpart.exe).
- "Microsoft Reserved Partition". Windows and GPT FAQ.
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