Volume serial number

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A volume serial number is a serial number assigned to a disk volume or tape volume. It originated in 1950s in mainframe computer operating systems. 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. For example "SYSRES" is often used for a system residence volume.

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. This identification system was created[citation needed] by Microsoft and IBM during their development of OS/2. The serial number is a 32-bit number determined by the date on the current computer[clarify] at the time of a disk's formatting. Previously, the method used to discern whether a disk was swapped was reading its volume label. However, it was not required to be unique or even non-empty. Many users had not given disks any name.

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