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In computer data storage, a volume or logical drive is a single accessible storage area with a single file system, typically (though not necessarily) resident on a single partition of a storage medium such as a solid-state drive (SSD) or hard disk drive (HDD). Although a volume might be different from a physical drive, it can still be accessed with an operating system's logical interface. However, a volume differs from a partition.

Although storage can be designed and configured in many different and complex ways, a simple volume describes the most basic configuration. It is one volume on one device with no redundancy, striping or spanning across devices.

The concept of volume applies to any type of storage medium. But, for historical reasons, the term disk is often used even for non-disk media. For example, the Windows Disk Management utility supports any type of media.

A volume is logically distinct from a partition. For example, a floppy disk might be accessible as a volume, even though it does not contain a partition, as floppy disks cannot be partitioned with most modern computer software. Also, an OS can recognize a partition without recognizing any volume associated with it, as when the OS cannot interpret the filesystem stored there. This situation occurs, for example, when Windows encounters a non-native partition, such as the ext4 filesystem commonly used with Linux. Another example occurs in the Intel world with the "Extended Partition". While these are partitions, they cannot contain a filesystem directly. Instead, "logical drives" (also known as volumes) must be created within them. This is also the case with NetWare volumes residing inside of a single partition. In short, volumes exist at the logical OS level, and partitions exist at the physical, media specific level. Sometimes there is a one-to-one correspondence, but this is not guaranteed.

In Windows Server 2008 and onward, the term "volume" is used as a superset that includes "partition".^[1][2][3]

It isn't uncommon to see a volume packed into a single file. Examples include ISO9660 disc images (CD/DVD images, commonly called "ISOs"), and installer volumes for Mac OS X (Apple Disk Image). As these volumes are files which reside within another volume, they certainly are not partitions.

This example concerns a Windows XP system with two physical hard disks. The first hard disk has two partitions, the second has only one. The first partition of the first hard disk contains the operating system. Mount points have been left at defaults.

Physical disk	Partition	Filesystem	Drive letter
Hard Disk 1	Partition 1	NTFS	C:
	Partition 2	FAT32	D:
Hard Disk 2	Partition 1	FAT32	E:

In this example,

• "C:", "D:", and "E:" are volumes.
• Hard Disk 1 and Hard Disk 2 are physical disks.
• Any of these can be called a "drive".

The characteristics of a volume differ by computing context.

In Windows, volumes are handled by the kernel and managed using the Disk Management utility or the diskpart command.

Unlike in a Unix-like system, Microsoft operating systems do not have a single root directory. As a result, the system assigns at least one path to each mounted volume, which will take one of two forms: either a drive letter (a single letter followed by a colon) such as "F:" or a mount-point on an NTFS volume having a drive letter, such as "C:\Music". In this case, the file "Track1.mp3" stored in the root directory of the mounted volume could be referred to via paths F:\Track1.mp3 or C:\Music\Track1.mp3, respectively.

In order to assign a mount point for a volume as a path within another volume, the following criteria must be met:

• The mounted-to volume must be formatted NTFS
• A directory must exist at the root path; as of Windows Vista, it can be any subdirectory in a volume
• That directory must be empty

By default, Windows assigns drive letters to all drives. It reserves "A:" and "B:" for floppy disk drives, whether present or not. It uses "C:" and subsequent letters for all other drives (e.g. SDD, HDD, CD, DVD). Because of this legacy convention, the operating system startup drive is most commonly assigned "C:", however this is not always the case. Since personal computers now no longer include floppies, and optical disc and other removable drives typically still start at "D:", letters A and B are available for manual assignment by a user with administrative privileges. This assignment will be remembered by the same OS on the same PC next time a removable volume is inserted, as long as there are no conflicts, and as long as the removable drive has not been reformatted on another computer (which changes its volume serial number), and as long as the OS has not been reinstalled on the computer.

In Windows, mount points can be managed via the Disk Management utility.

More than one drive letter can refer to a single volume, as when using the SUBST command.

Removing drive letters or mount-points for a drive may break some programs, as some files may not be accessible under the known path. For example, if a program is installed at "D:\Program Files\Some Program", it may expect to find its data files at "D:\Program Files\Some Program\Data". If the logical disk previously called "D:" has its drive letter changed to "E:", "Some Program" won't be able to find its data at "D:\Program Files\Some Program\Data", since the drive letter "D:" no longer represents that volume.

In a Linux system, volumes are usually handled by the Logical Volume Manager or the Enterprise Volume Management System and manipulated using mount(8).

In Unix-like systems, volumes other than the boot volume have a mount-point somewhere within the filesystem, represented by a path. Logically, the directory tree stored on the volume is grafted in at the mountpoint. By convention, mount-points will often be placed in a directory called '/mnt', though '/media' and other terms are sometimes used.

To use a given path as a mount-point for another volume, a directory must exist at that path.

Unix-like systems use the mount command to manipulate mount points for volumes. For example, if a CD-ROM drive containing a text file called 'info.txt' was mounted at '/mnt/iso9660', the text file would be accessible at '/mnt/iso9660/info.txt'.

Files within a volume can generally be moved to any other place within that volume by manipulating the filesystem, without moving the actual data. However, if a file is to be moved outside the volume, the data itself must be relocated, which is a much more expensive operation.

In order to better visualize this concept, one might consider the example of a large library. If a non-fiction work is originally classified as having the subject "plants", but then has to be moved to the subject "flora", one does not need to refile the book, whose position on the shelf would be static, but rather, one needs only to replace the index card. However, to move the book to another library, adjusting index cards alone is insufficient. The entire book must be moved.

Often, a volume is identified within a system by either or both a user-assignable and more human-readable identifier and a more fixed and globally-unique identifier that may be less human-readable. Identifier attributes and use varies by computing context.

Use of volume serial numbers originated in the 1950s with mainframes. In the OS/360 line, it user-configurable, has a maximum length of six characters, is uppercase and must start with a letter. For example, "SYSRES" is often used for a system residence volume. Operating systems may use the volume serial number as mountpoint name.^[4]

A volume label is a name assigned to a volume and is generally user-assignable. In the FAT filesystem, the volume label was traditionally restricted to 11 characters (reflecting the 8.3 restriction although not divided into name and extension) even when long file name was enabled, stored as an entry within a disk's root directory with a special volume-label attribute bit set, and also copied to an 11-byte field within the Extended BIOS Parameter Block of the disk's boot sector. The label is always stored as uppercase in FAT and VFAT filesystems, and cannot contain special characters that are also disallowed for regular filenames. In the NTFS filesystem, the length of its volume label is restricted to 32 characters, and can include lowercase characters and even Unicode. In the exFAT filsystem, the length of its volume label is also restricted to 11 characters, but can include lowercase and Unicode characters. The label command supports changing the label in DOS, Windows, and OS/2. In Windows Explorer, F2 can be pressed while the volume is highlighted, or a right-click on the name allows it to be renamed.

A volume serial number is a serial number assigned to a storage medium that is generally both unique and not editable by the user. It provides a consistent and reliable identifier for the volume. In particular, it allows for determining when a volume has been added to or removed from a system. Formatting a volume typically changes the serial number, but relabeling does not.^[5] In the FAT and NTFS file systems, a volume serial number is used to determine if a volume is present in a drive or not, and to detect if it was exchanged with another one. This identification system was designed during their development of OS/2.^[6] It was introduced in MS-DOS 4.01 in 1988. The serial number is a 32-bit number determined by the real-time clock reading of the host computer when the volume is formatted. Previously, determination of whether a volume was swapped was done by reading the volume label. However, even at that time the volume label was both optional and not required to be unique which resulted in incorrect detection of media changes. The vol Command Prompt command displays the label and serial number of the volume associated with the working directory.

• MSDN's article on Hard Links and Junctions