1.1 Glossary

This document uses the following terms:

active partition: A partition on a master boot record (MBR) disk that becomes the system partition at system startup if the basic input/output system (BIOS) is configured to select that disk for startup. An MBR disk can have exactly one active partition. The active partition is stored in the partition table on the disk. GUID partitioning table (GPT) disks do not have active partitions. See also master boot record (MBR), system partition, and partition table.

active volume: For volumes that consist of single partitions, active volume is synonymous with active partition. For volumes that consist of multiple partitions, active volume refers to a volume in which one of the partitions is an active partition (generally mirrored volumes because partitions on striped volumes or RAID-5 volumes do not have complete copies of volume data). See also active partition.

allocation unit size: The size (expressed in bytes) of the units used by the file system to allocate space on a disk for the file system used by the volume. The size, in bytes, must be a power of two and must be a multiple of the size of the sectors on the disk. Typical allocation unit sizes of most file systems range from 512 bytes to 64 KB.

attach: To create and expose a disk device object for a virtual disk on the operating system. For example, when a user creates a virtual disk, a virtual disk file is allocated as the backing store for the virtual disk. However, creating the virtual disk does not cause an operating system disk object to be created and exposed; attaching does this.

backing store: The virtual disk file that stores the data for a virtual disk.

basic disk: A disk on which each volume can be composed of exclusively one partition.

basic provider: A virtual disk service (VDS) provider that manages basic disks.

BitLocker: BitLocker Drive Encryption. A Microsoft-developed feature appearing in Windows Vista operating system that provides encryption for an entire volume.

boot configuration file: A file that contains a list of paths to boot partitions. On architectures featuring the Extensible Firmware Interface (EFI), the boot configuration file can be stored on other nonvolatile media, such as nonvolatile random access memory (NVRAM). On all other architectures, it resides in the system partition.

boot loader: An architecture-specific file that loads the operating system on the boot partition as specified by the boot configuration file.

boot partition: A partition containing the operating system.

boot volume: See boot partition.

bus: Computer hardware to which peripheral devices can be connected. Messages are sent between the CPU and the peripheral devices using the bus. Examples of bus types include SCSI, USB, and 1394.

Challenge-Handshake Authentication Protocol (CHAP): A protocol for user authentication to a remote resource. For more information, see [RFC1994] and [RFC2759].

cluster: A group of computers that are able to dynamically assign resource tasks among nodes in a group.

Cluster Shared Volume File System (CSVFS): Cluster Shared Volume File System is a technology that simplifies configuration and management of clustered virtual machines by enabling multiple clustered virtual machines to use the same LUN while still allowing independent failover capability.

cluster size: See allocation unit size.

Compact Disc File System (CDFS): A file system used for storing files on CD-ROMs.

Component Object Model (COM): An object-oriented programming model that defines how objects interact within a single process or between processes. In COM, clients have access to an object through interfaces implemented on the object. For more information, see [MS-DCOM].

crash dump file: A file that can be created by an operating system when an unrecoverable fault occurs. This file contains the contents of memory at the time of the crash and can be used to debug the problem creator.

cylinder: The set of disk tracks that appear in the same location on each platter of a disk.

detach: To delete a virtual disk object from the operating system. See attach.

differencing chain: The set of virtual disks defined by a differencing disk and its parent or parents. For example, consider a scenario in which differencing disk A's parent is differencing disk B, and differencing disk B's parent is virtual disk C. In this example, disks A, B, and C create a differencing chain where disk A is the child and disks B and C are both parents.

differencing disk: The current state of a virtual disk represented as a set of modified blocks storing differences from the parent virtual disk. A differencing disk is not independent; it depends on the parent virtual disk to be fully functional. A differencing disk can be the parent to another differencing disk. See also differencing chain.

disk: A persistent storage device that can include physical hard disks, removable disk units, optical drive units, and logical unit numbers (LUNs) unmasked to the system.

disk extent: A contiguous set of one or more disk sectors. A disk extent can be used as a partition or part of a volume, or it can be free, which indicates that it is not in use or that it might be unusable for creating partitions or volumes.

disk group: In the context of dynamic disks, this term describes a logical grouping of disks.

disk pack: See disk group.

disk quorum: The minimum number of disks in a disk group that is required to enable the online status of a disk group. A disk quorum is defined as n/2 + 1, where n is the total number of disks in the group. A disk quorum prevents disk groups from gaining online status on more than one computer.

disk signature: A unique identifier for a disk. For a master boot record (MBR)-formatted disk, this identifier is a 4-byte value stored at the end of the MBR, which is located in sector 0 on the disk. For a GUID partitioning table (GPT)-formatted disk, this value is a GUID stored in the GPT disk header at the beginning of the disk.

disk type: A disk that is hardware-specific. A disk can only communicate with the CPU using a bus of matching type. Examples of bus types include SCSI, USB, and 1394.

Distributed Component Object Model (DCOM): The Microsoft Component Object Model (COM) specification that defines how components communicate over networks, as specified in [MS-DCOM].

drive letter: One of the 26 alphabetical characters A-Z, in uppercase or lowercase, that is assigned to a volume. Drive letters serve as a namespace through which data on the volume can be accessed. A volume with a drive letter can be referred to with the drive letter followed by a colon (for example, C:).

dynamic disk: A disk on which volumes can be composed of more than one partition on disks of the same pack, as opposed to basic disks where a partition and a volume are equivalent.

dynamic provider: A Virtual Disk Service (VDS) provider that manages dynamic disks.

dynamic volume: A volume on a dynamic disk.

EUI-64: The IEEE-defined 64-bit extended unique identifier (EUI-64). EUI-64 is a concatenation of the 24-bit company_id value by the IEEE Registration Authority and a 40-bit extension identifier that is assigned by the organization with that company_id assignment. For more information, see [EUI64].

extended partition: A construct that is used to partition a disk into logical units. A disk can have up to four primary partitions or up to three primary partitions and one extended partition. The extended partition can be further subdivided into multiple logical drives.

Extensible Firmware Interface (EFI): A system developed by Intel designed to replace the BIOS. It is responsible for bootstrapping the operating system on GUID partitioning table disks.

FAT file system: A file system used to organize and manage files. The file allocation table (FAT) is a data structure that the operating system creates when a volume is formatted by using FAT or FAT32 file systems. The operating system stores information about each file in the FAT so that it can retrieve the file later.

FAT32 file system: A derivative of the file allocation table (FAT) file system. FAT32 supports smaller cluster sizes and larger volumes than FAT, which results in more efficient space allocation on FAT32 volumes. FAT32 uses 32-bit addressing.

fault-tolerant: The ability of computer hardware or software to ensure data integrity when hardware failures occur. Fault-tolerant features appear in many server operating systems and include mirrored volumes and RAID-5 volumes. A fault-tolerant volume maintains more than one copy of the volume's data. In the event of disk failure, a copy of the data is still available.

fiber channel bus: A bus technology that uses optical fiber for communication.

file allocation table (FAT): A data structure that the operating system creates when a volume is formatted by using FAT or FAT32 file systems. The operating system stores information about each file in the FAT so that it can retrieve the file later.

file system: A set of data structures for naming, organizing, and storing files in a volume. NTFS, FAT, and FAT32 are examples of file system types.

file system label: A non-unique string of characters that the file system assigns to the volume, as specified by the user when formatting the volume.

foreign: A dynamic disk group that is not part of a machine's primary disk group. The term foreign denotes "foreign to this machine". Foreign disk and foreign disk groups are not online. This means that these disks may not be configured and no data input/output (I/O) to the disks or the volumes on the disks is permitted.

format: To submit a command for a volume to write metadata to the disk, which is used by the file system to organize the data on the disk. A volume is formatted with a specific file system.

free space: Space on a disk not in use by any volumes, primary partitions, or logical drives.

full-volume encryption: Encryption of the entire volume, including user files, system files, swap files, and hibernation files.

globally unique identifier (GUID): A term used interchangeably with universally unique identifier (UUID) in Microsoft protocol technical documents (TDs). Interchanging the usage of these terms does not imply or require a specific algorithm or mechanism to generate the value. Specifically, the use of this term does not imply or require that the algorithms described in [RFC4122] or [C706] must be used for generating the GUID. See also universally unique identifier (UUID).

GUID partition table (GPT): A disk-partitioning scheme that is used by the Extensible Firmware Interface (EFI). GPT offers more advantages than master boot record (MBR) partitioning because it allows up to 128 partitions per disk, provides support for volumes up to 18 exabytes in size, allows primary and backup partition tables for redundancy, and supports unique disk and partition IDs through the use of globally unique identifiers (GUIDs). Disks with GPT schemes are referred to as GPT disks.

hard disk: A peripheral device that provides persistent data storage and does not have removable media.

host bus adapter (HBA): A hardware device that adapts the signals of one electronic interface to another.

HRESULT: An integer value that indicates the result or status of an operation. A particular HRESULT can have different meanings depending on the protocol using it. See [MS-ERREF] section 2.1 and specific protocol documents for further details.

import target: An iSCSI target with which the LUNs being imported to the subsystem are associated.

interface: A specification in a Component Object Model (COM) server that describes how to access the methods of a class. For more information, see [MS-DCOM].

Interface Definition Language (IDL): The International Standards Organization (ISO) standard language for specifying the interface for remote procedure calls. For more information, see [C706] section 4.

Internet SCSI (iSCSI): For terms related to iSCSI, see [RFC3720].

iSCSI initiator: A client of a SCSI interface. An iSCSI initiator issues SCSI commands to request services from components, which are logical units of a server known as a "target". For more information, see [RFC3720] section 1.

iSCSI initiator adapter: The hardware that allows an iSCSI initiator to communicate with other computers on the network. For more information, see [RFC3720] section 9.1.

iSCSI initiator portal: The component of an iSCSI initiator that has a TCP/IP network address and that can be used by an iSCSI node in that network entity for the connections in one of its iSCSI sessions. For more information, see [RFC3720] section 3.4.

iSCSI session: A group of TCP connections that link an iSCSI initiator with a target. For more information, see [RFC3720] section 3.4.

iSCSI target: A server of a SCSI interface, or a logical unit of a server that responds to SCSI command requests from an iSCSI initiator for servers that contain multiple SCSI target ports, device servers, and associated logical units. For more information, see [RFC3720] section 1.

Logical Disk Manager (LDM): A subsystem of Windows that manages dynamic disks. Dynamic disks contain a master boot record (MBR) at the beginning of the disk, one LDM partition, and an LDM database at the end. The LDM database contains partitioning information used by the LDM.

Logical Disk Manager Administrative Service: The part of Disk Management Services that implements the disk and volume management operations (see [MSDN-VOLMAN]). Disk Management Services provides support for disk and volume management operations and monitors disk arrivals and removals and other changes in the storage subsystem.

logical unit number (LUN): A number that is used to identify a disk on a given disk controller.

master boot record (MBR): Metadata such as the partition table, the disk signature, and the executable code for initiating the operating system boot process that is located on the first sector of a disk. Disks that have MBRs are referred to as MBR disks. GUID partitioning table (GPT) disks, instead, have unused dummy data in the first sector where the MBR would normally be.

mirrored volume: A fault-tolerant volume that maintains two or more copies of the volume's data. In the event that a disk is lost, at least one copy of the volume's data remains and can be accessed.

mount point: See mounted folder.

NT file system (NTFS): A proprietary Microsoft file system. For more information, see [MSFT-NTFS].

NULL GUID: A GUID of all zeros.

offline: An operational state applicable to volumes and disks. In the offline state, the volume or disk is unavailable for data input/output (I/O) or configuration.

online: An operational state applicable to volumes and disks. In the online state, the volume or disk is available for data input/output (I/O) or configuration.

opnum: An operation number or numeric identifier that is used to identify a specific remote procedure call (RPC) method or a method in an interface. For more information, see [C706] section or [MS-RPCE].

pack: See disk group.

page file or paging file: A file that is used by operating systems for managing virtual memory.

partition: In the context of hard disks, a logical region of a hard disk. A hard disk may be subdivided into one or more partitions.

partition table: An area of a disk that is used to store metadata information about the partitions on the disk. See also, GUID partitioning table (GPT).

partition type: A value indicating the partition's intended use, or indicating the type of file system on the partition. For example, partition type 0x07 indicates that the partition is formatted with the NTFS file system. Original equipment manufacturers can designate a partition type of 0x12 to indicate that manufacturer-specific data is stored on the partition.

path: When referring to a file path on a file system, a hierarchical sequence of folders. When referring to a connection to a storage device, a connection through which a machine can communicate with the storage device.

plex: See volume plex.

quick format: A formatting that does not zero the data sectors on the volume at the time the file system metadata is created.

RAID column: A RAID construct for organizing disks and volumes.

RAID-0: A RAID volume that stripes its data across multiple RAID columns. Also called a striped volume.

RAID-1: See mirrored volume.

RAID-5: A fault-tolerant volume that maintains the volume's data across multiple RAID columns. Fault tolerance is provided by writing parity data for each stripe. In the event that one disk encounters a fault, that disk's data can be reconstructed using the parity data located on the other disks.

read-only: An attribute of storage media that denotes that the media is not available to be written.

redundant arrays of independent disks (RAID): A set of disk-organization techniques that is designed to achieve high-performance storage access and availability.

reference count: An integer value that is used to keep track of a Component Object Model (COM) object. When an object is created, its reference count is set to 1. Every time an interface is bound to the object, its reference count is incremented; when the interface connection is destroyed, the reference count is decremented. The object is destroyed when the reference count reaches zero. All interfaces to that object are then invalid.

region: See disk extent.

remote procedure call (RPC): A communication protocol used primarily between client and server. The term has three definitions that are often used interchangeably: a runtime environment providing for communication facilities between computers (the RPC runtime); a set of request-and-response message exchanges between computers (the RPC exchange); and the single message from an RPC exchange (the RPC message).  For more information, see [C706].

removable media: Any type of storage that is not permanently attached to the computer. A persistent storage device stores its data on media. If the media can be removed from the device, the media is considered removable. For example, a floppy disk drive uses removable media.

reparse point: An attribute that can be added to a file to store a collection of user-defined data that is opaque to NTFS or ReFS. If a file that has a reparse point is opened, the open will normally fail with STATUS_REPARSE, so that the relevant file system filter driver can detect the open of a file associated with (owned by) this reparse point. At that point, each installed filter driver can check to see if it is the owner of the reparse point, and, if so, perform any special processing required for a file with that reparse point. The format of this data is understood by the application that stores the data and the file system filter that interprets the data and processes the file. For example, an encryption filter that is marked as the owner of a file's reparse point could look up the encryption key for that file. A file can have (at most) 1 reparse point associated with it. For more information, see [MS-FSCC].

Resilient File System (ReFS): The Resilient File System is a file system that provides maximum data availability, scalability, and data integrity despite hardware or software failures. ReFS is frequently used together with Storage Spaces.

RPC protocol sequence: A character string that represents a valid combination of a remote procedure call (RPC) protocol, a network layer protocol, and a transport layer protocol, as described in [C706] and [MS-RPCE].

SCSI name string identifier: An identifier string that is used to identify a SCSI bus device. For more information, see [SPC-3].

sector: The smallest addressable unit of a disk.

secure digital (SD) bus: A computer bus that transfers data between a host controller and a secure digital card, which is a non-volatile memory card format commonly used in a portable device.

shadow copy: A duplicate of data held on a volume at a well-defined instant in time.

shared secret: A piece of data that is known only to the security principal and an authenticating authority; for example, a user and a domain controller. It is used to prove the principal's identity. A password is a common example of a shared secret. Also called a "secret key".

small computer system interface (SCSI) bus: A standard for connecting peripheral devices to a computer. A SCSI bus is an implementation of this standard.

snapshot: The point in time at which a shadow copy of a volume is made.

Storage Spaces: Storage Spaces enables virtualization of storage by grouping industry-standard disks into storage pools, and then allocating storage from the available capacity in the storage pools.

subsystem: A storage device that coordinates and controls the operation of one or more disk drives.

super floppy: A high-capacity floppy disk. A super floppy layout is one in which there is no MBR, so there is no partition table. The entire disk (from start to end) is one giant partition.

system partition: A partition that contains the boot loader needed to invoke the operating system on the boot partition. A system partition must also be an active partition. It can be, but is not required to be, the same partition as the boot partition.

system volume: For volumes that consist of single partitions, system volume is synonymous with system partition. For volumes that consist of multiple partitions, system volume refers to a volume in which one of the partitions is a system partition (generally mirrored volumes, because partitions on striped or RAID-5 volumes do not have complete copies of volume data). See also system partition.

track: Any of the concentric circles on a disk platter over which a magnetic head (used for reading and writing data on the disk) passes while the head is stationary but the disk is spinning. A track is subdivided into sectors, upon which data is read and written.

unallocated disk: A disk that is visible to the local machine but is not formatted with a recognized partitioning format such as master boot record (MBR) or GUID partitioning table (GPT).

Universal Disk Format (UDF): A type of file system for storing files on optical media.

universal serial bus (USB): An external bus that supports Plug and Play installation. It allows devices to be connected and disconnected without shutting down or restarting the computer.

universally unique identifier (UUID): A 128-bit value. UUIDs can be used for multiple purposes, from tagging objects with an extremely short lifetime, to reliably identifying very persistent objects in cross-process communication such as client and server interfaces, manager entry-point vectors, and RPC objects. UUIDs are highly likely to be unique. UUIDs are also known as globally unique identifiers (GUIDs) and these terms are used interchangeably in the Microsoft protocol technical documents (TDs). Interchanging the usage of these terms does not imply or require a specific algorithm or mechanism to generate the UUID. Specifically, the use of this term does not imply or require that the algorithms described in [RFC4122] or [C706] must be used for generating the UUID.

user-defined function (UDF): A function that is coded in a Microsoft Visual Basic for Applications (VBA) module, macro sheet, add-in, or Excel Linked Library (XLL). A UDF can be used in formulas to return values to a worksheet, similar to built-in functions.

VDS: Virtual Disk Service (VDS) Protocol.

VDS object: An instance of a class that exposes one or more DCOM interfaces to query or configure the VDS service, the operating system device (such as a disk or volume), or the concept (such as a software provider) that the object represents. Each object has an associated type that indicates the type of device or concept that it represents. Unless otherwise indicated, the term "object" refers to a VDS object.

virtual disk: A disk that does not have a physical mechanical counterpart to it, and is not exposed as a hardware array LUN. It is a disk that uses a file to store its data. When this file is exposed to the operating system as a disk device, the exposed disk device emulates and, for all intents and purposes, behaves like a physical disk.

virtual disk file: The file that is the backing store for a virtual disk. This file may be exposed to an operating system as a disk device. The exposed disk device is referred to as a virtual disk.

virtual disk provider: A VDS object that allows query and management of virtual disks on a system.

Virtual Disk Service (VDS): If the term is used as a noun, VDS refers to the service component that runs on the server. If VDS is used as an adjective, it refers to the protocol that is specified in this document (which the service uses to communicate with clients).

Virtual Disk Service (VDS) session: The point at which a client receives an instance of the VDS service object until the point at which it releases it. Unless otherwise indicated, the term session refers to a VDS session.

virtual hard disk: Same as a virtual disk.

volume: A group of one or more partitions that forms a logical region of storage and the basis for a file system. A volume is an area on a storage device that is managed by the file system as a discrete logical storage unit. A partition contains at least one volume, and a volume can exist on one or more partitions.

volume label: See file system label.

volume manager: A system component that manages communication and data transfer between applications and disks.

volume plex: A member of a volume that represents a complete copy of data stored. For instance, mirrored volumes have more than one plex.

volume plex member: A RAID construct for organizing disks and volumes. Also called a RAID column.

Windows Event log: An audit trail created by Windows instrumentation manifest to monitor the health of the operating system and to help troubleshoot issues when they arise. The event logs can be browsed and managed by Windows Event Viewer.

Windows Preinstallation Environment (Windows PE): A minimal Windows system environment that provides limited services. It provides the minimum set of features that are required to run the operating system setup, perform system recovery, access and install operating systems from the network, script basic repetitive tasks, and validate hardware.

MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.