A Microsoft Reserved Partition (MSR) is a partition of a

data storage device Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are cons ...

, which is created to reserve a portion of disk space for possible subsequent use by a

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

installed on a separate partition. No meaningful data is stored within the MSR; though from the MSR, chunks may be taken for the creation of new partitions, which themselves may contain data structures. The

GUID Partition Table The GUID Partition Table (GPT) is a standard for the layout of partition tables of a physical computer storage device, such as a hard disk drive or solid-state drive, using universally unique identifiers, which are also known as globally unique ...

(GPT) label for this partition type is E3C9E316-0B5C-4DB8-817D-F92DF00215AE.

Purpose

Formerly, on disks formatted using the

master boot record A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The concept of MB ...

(MBR) partition layout, certain software components used hidden sectors of the disk for data storage purposes. For example, the

Logical Disk Manager The Logical Disk Manager (LDM) is an implementation of a logical volume manager for Microsoft Windows NT, developed by Microsoft and Veritas Software. It was introduced with the Windows 2000 operating system, and is supported in Windows XP, ...

(LDM), on

dynamic disk The Logical Disk Manager (LDM) is an implementation of a logical volume manager for Microsoft Windows NT, developed by Microsoft and Veritas Software. It was introduced with the Windows 2000 operating system, and is supported in Windows XP, Windo ...

s, stores metadata in a 1 MB area at the end of the disk which is not allocated to any partition. The

UEFI UEFI (Unified Extensible Firmware Interface) is a set of specifications written by the UEFI Forum. They define the architecture of the platform firmware used for booting and its interface for interaction with the operating system. Examples ...

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 software-component-specific partitions can be allocated from a portion of the space reserved in the MSR partition.

Size

Beginning in Windows 10, the minimum size of the MSR is 16 MB which the installer allocates by default.

Location

The MSR should be located after the EFI System Partition (ESP) and any

OEM An original equipment manufacturer (OEM) is generally perceived as a company that produces non-aftermarket parts and equipment that may be marketed by another manufacturer. It is a common industry term recognized and used by many professional or ...

service partitions, but it must be located before any primary partitions of bootable

s. Microsoft expects an MSR to be present on every GPT disk, and recommends it to be created as the disk is initially partitioned.

References

Disk partitions Windows NT architecture {{Compu-storage-stub

Purpose

Size

Location

See also

References