File Systems

Windows supports four types of file systems on readable/writable disks: the NTFS file system and three file allocation table (FAT) file systems: FAT12, FAT16 and FAT32.

Windows also supports two types of file systems on CD-ROM and digital video disk (DVD) media: Compact Disc File System (CDFS) and Universal Disk Format (UDF).

The structures of the volumes formatted by each of these file systems, as well as the way each file system organizes data on the disk, are significantly different.


The FAT file system locates the file allocation table near the beginning of the volume. FAT12 is the original implementation of FAT and is intended for very small media (floppy disks). FAT16 was designed for small disks and simple directory structures. FAT32 allowed users to create large volumes on large disks.

Two copies of the file allocation table are stored on the volume. In the event that one copy of the file allocation table is corrupted, the other is used. The file allocation table is stored in a byte offset specified in the FAT boot sector's BIOS Parameter Block (BPB) so that the files needed to start the system can be located.


NTFS, the preferred native file system for Windows 2000/XP/Vista/7, is a much more sophisticated, robust, and secure file system than any of the FAT file systems. The NTFS data structures allow you to take advantage of new features, such as:

Recoverability NTFS is a recoverable file system. A user seldom needs to run a disk repair program on an NTFS volume. NTFS guarantees the consistency of the volume by using standard transaction logging and recovery techniques. In the event of a system failure, NTFS uses its log file and checkpoint information to automatically restore the consistency of the file system.

Compression NTFS supports compression on volumes, directories, and files. Files that are compressed on an NTFS volume can be read and written by any Windows-based application without first being decompressed by another program; decompression happens automatically during the file read. The file is compressed again when it is closed or saved.

Encryption The Encrypting File System (EFS) provides the core file encryption technology used to store encrypted files on NTFS volumes. EFS keeps files safe from intruders who might gain unauthorized physical access to sensitive, stored data (for example, by stealing a portable computer or external disk drive).

Security On NTFS volumes, you can set permissions on shares, directories, and files that specify which groups and users have access, and what level of access is permitted. NTFS file and directory permissions apply to users working on the local computer and to users accessing the file over the network from a shared directory. You can also set share permissions that operate on network shares in combination with file and directory permissions.

Disk quotas You can use disk quotas to monitor and limit disk-space use.

Reparse points Reparse points are file system objects in NTFS that can be applied to NTFS files or directories. A file or directory that contains a reparse point acquires additional behavior not present in the underlying file system. Reparse points are used by many of the new storage features in Windows 2000, including volume mount points.

Volume mount points Based on reparse points, volume mount points allow administrators to graft access to the root of one local volume onto the directory structure of another local volume.

Sparse files Sparse files allow programs to create very large files but consume disk space only as needed.

Compact Disc File System (CDFS)

Windows provides support for the ISO 9660-compliant compact disc file system (CDFS), which supports long file names.

Universal Disk Format (UDF)

UDF is a file system defined by the Optical Storage Technology Association (OSTA). UDF is compliant with the ISO 13346 standard and is the successor to the CD-ROM file system (CDFS or ISO 9660).

UDF is targeted for removable disk media like DVD, CD, and Magneto-Optical (MO) discs. Since UDF is based on open standards, it is intended to facilitate data interchange between operating systems, and between consumer devices.