The USN Journal (Update Sequence Number Journal), or Change Journal, is a feature of the Windows NT file system (

NTFS New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred fil ...

) which maintains a record of changes made to the

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...

. It is not to be confused with the journal used for the NTFS file system journaling. When

Windows 2000 Windows 2000 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It was the direct successor to Windows NT 4.0, and was released to manufacturing on December 15, 1999, and was officiall ...

was released,

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...

created

version 3.0, which included several new features and improvements over older versions of the file system. One of these was a new system management feature that is very useful for certain types of applications. Under Windows 2000, NTFS 3.0

partitions Partition may refer to: Computing Hardware * Disk partitioning, the division of a hard disk drive * Memory partition, a subdivision of a computer's memory, usually for use by a single job Software * Partition (database), the division of a ...

can be set to keep track of changes to files and directories on the

, providing a record of when and what was done to the various objects. When enabled, the system records all changes made to the volume in the USN Journal, which is the name also used to describe the feature itself. One journal is maintained for each NTFS volume and stored in the NTFS metafile named $Extend\$UsnJrnl. It begins as an empty

file File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...

. Whenever a change is made to the volume, a record is added to the file. Each record is identified by a

64-bit In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A compu ...

Update Sequence Number or USN (for this reason Change Journals are sometimes called USN Journals). Each record in the Change Journal contains the USN, the name of the file, and information about what the change was. The Change Journal describes the changes that took place using bit flags (e.g. USN_REASON_DATA_OVERWRITE), therefore it does not include all the

data In the pursuit of knowledge, data (; ) is a collection of discrete Value_(semiotics), values that convey information, describing quantity, qualitative property, quality, fact, statistics, other basic units of meaning, or simply sequences of sy ...

or details associated with the change. For this reason the Change Journal cannot be used to undo operations on files within NTFS.

Uses

The USN Journal is used by the

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feature introduced in

Windows 8 Windows 8 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on August 1, 2012; it was subsequently made available for download via MSDN and TechNet on August 15, 2012, and later to ...

to determine which files have changed since the last backup so that only files that have changed are added to the history so far.

References

External links

* * * * {{DEFAULTSORT:Usn Journal Computer file systems Windows disk file systems