NTFS Documentation: Glossary

Attribute

Block

In Linux terminology, this is a cluster.

Block device

In Linux terminology, this is a storage unit.

Cluster

The minimum allocation unit. Clusters are a fixed power of 2 of the sector size (called the cluster factor), and their size can be between 512 bytes and 4 KB (Sometimes 64 KB, but 4 KB is the largest cluster size that the current NTFS compression engine can operate with. That limit may be related to the 4 KB page size used on the Intel i386 CPU). This size can be set with the Windows NT® format utility, whose default is:

Volume size	Cluster size
1 to 512 MB	Sector size
512 MB to 1 GB	1 KB
1 GB to 2 GB	2 KB
more than 2 GB	4 KB

Directory

File

In the NTFS terminology, a file can be a normal file, directory (like in Linux) or a system file.

File reference

Filesystem

The physical structure an operating system uses to store and organize files on a storage unit. A common filesystem is FAT (used by DOS®).

Fork

HFS

The MacOS® filesystem.

HPFS

The OS/2® filesystem. Remember: once upon a time, OS/2® had to be the operating system developped by both IBM and Microsoft. There was a break between the 2 giants. IBM continued to develop OS/2® (it became OS/2 Warp®), and that explains why OS/2® knows how to execute Windows® applications. Microsoft decided to make its own operating system: Windows NT®. HPFS design influenced NTFS design, so the 2 filesystems share many features.

Inode

LCN

An acronym which stands for Logical Cluster Number. The LCN is a notion relative to a volume. LCNs are ordered from the first cluster (LCN 0) of a volume to the last one.

Metadata

Data on the storage unit used by the filesystem only, as a frame to access user data. Metadata constitutes the structure of the filesystem). Metadata examples from various filesystems include FATs, inode tables, free block lists, free block bitmaps, logging areas, and the superblock.

MFT

NTFS

Nibble

Half of a byte (4 bits).

POSIX

An acronym (expected to be pronounced pahz-icks, as in positive. It was suggested by Richard M. Stallman, you know, the guy who is everywhere:) for Portable Operating System Interface. It is a set of international standards (ISO/IEC 9945-1:1996(E), ANSI/IEEE Std 1003.1 1996 Edition) to interface with Unix®-like exploitation systems, e.g. Linux. NTFS does not support Unix®-like device files. If 'devfs' ever gets written, Linux will be able to use NTFS as the root partition. Actually, one could introduce a new file attribute, say POSIX_ATTRIBUTES, which would store large uid, gid, flags, and, in the case of character or block devices, large major and minor device numbers.

Roll-back

Run

Sector

Unit of data on the physical storage unit. The storage controller can only access data in multiples of this unit. A sector is usually 512 bytes, but can be 1 KB on certain Asian hard disks.

Stream

Transaction

A transaction on a system is a set of operations (on that system) that constitutes a unit. This unit can't be divided.
Before the transaction, the state of the system is well defined. During the transaction, it is undefined. After the transaction, it is well defined again. A transaction can't be half-realized: if no operation fails, the transaction is realized. If on the contrary an error occurs in one or more of the operations, the transaction is not realized. A set of (even atomic) operations is not atomic by definition. A transaction is a model that provides a kind of atomicity to this set of operations.

Unicode

International character set coded on 16 bits (ASCII is coded on 7 bits and Latin-1 coded on 8 bits). Unicode can represent every symbol of almost every language in the world.

Update sequence

VCN

Volume

A logical NTFS partition. It is a group of physical partitions (see the fdisk utility, you can set up mirroring and stripping) that act as one (somewhat like the Linux md block devices).