Volume (computing)

Although a volume might be different from a physical disk drive, it can still be accessed with an operating system's logical interface.

This situation occurs, for example, when Windows NT-based OSes encounter disks with non-Microsoft OS partitions, such as the ext4 filesystem commonly used with Linux.

In Microsoft Windows Server 2008 and onward, the term "volume" is used as a superset that includes "partition" as well.

This example concerns a Windows XP system with two physical hard disks.

As a result, Windows will assign at least one path to each mounted volume, which will take one of two forms: In these two examples, a file called "Track 1.mp3" stored in the root directory of the mounted volume could be referred to as "F:\Track 1.mp3" or "C:\Music\Track 1.mp3", respectively.

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 can be most conveniently accessed through "Computer Management" in the "Administrative Tools" section of the Control Panel.

In the FAT filesystem, the volume label was traditionally restricted to 11 characters (reflecting the 8.3 restrictions, but not divided into name and extension fields) 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.

NTFS partitions have the System Volume Information directory, whose creation timestamp is set when Windows creates the partition, or when it first recognizes a repartitioning (the creation of a new volume) by a separate disk utility.

In contrast to the label, the volume serial number is generally unique and is not normally changed by the user, and thus acts as a more consistent and reliable identifier of when a volume has been changed (as when a disk is removed and another inserted).

In OS/360 line it is human-configurable, has a maximum length of six characters, is in uppercase, must start with a letter, and identifies a volume to the system in unique manner.

In FAT and NTFS file systems, a volume serial number is a feature used to determine if a disk is present in a drive or not, and to detect if it was exchanged with another one.

Previously, determination by the OS of whether a disk was swapped was done by reading the drive's volume label.