Flie Systems (FAT & NTFS)

File Allocation Table (FAT) is the name of a computer file system architecture and a family of industry standard file systems utilizing it.

The FAT file system is technically relatively simple yet robust. It offers reasonably good performance even in light-weight implementations and is therefore widely adopted and supported by virtually all existing operating systems for personal computers. This makes it a well-suited format for data exchange between computers and devices of almost any type and age from the early 1980s up to the present.

Originally designed in the late 1970s for use on floppy disks, it was soon adapted and used almost universally on hard disksthroughout the DOS and Windows 9x eras for two decades. With the introduction of more powerful computers and operating systemsits use on hard drives has since started to decline, but it continues to be used on many computer systems.

Today, FAT file systems are still commonly found on floppy disks, solid-state memory cards, flash memory cards, and on many portable and embedded devices.

The name of the file system originates from the file system's prominent usage of an index table, the FAT, statically allocated at the time of formatting. The table contains entries for each cluster, a contiguous area of disk storage. Each entry contains either the number of the next cluster in the file, or else a marker indicating end of file, unused disk space, or special reserved areas of the disk. The root file directory of the disk contains the number of the first cluster; the operating system can then traverse the FAT table, looking up the cluster number of each successive part of the disk file as a cluster chain until the end of the file is reached.

As disk drives have evolved, the maximum number of clusters has significantly increased, and so the number of bits used to identify each cluster has grown. The successive major versions of the FAT format are named after the number of table element bits: 12 (FAT12), 16 (FAT16), and 32 (FAT32).

FAT was also commonly used on hard disks throughout the DOS and Windows 9x eras, but its use on hard drives has declined since the introduction of Windows XP, which primarily uses the newer NTFS. FAT is still used in hard drives expected to be used by multiple operating systems, such as in shared Windows and Linux environments.

Due to the widespread use of FAT formatted media since its introduction many operating systems have provided support for FAT and subsequently VFAT and FAT32 through official or third-party file system handlers. For example, Mac OS 9 and Mac OS X also support FAT file systems on volumes other than the boot disk. AmigaOS supports FAT through the CrossDOS file system.

For many purposes, the NTFS file system is superior to FAT in terms of features and reliability; its main drawbacks are the size overhead for small volumes and the very limited support by anything other than the NT-based versions of Windows, since the exact specification is a trade secret of Microsoft. The availability of NTFS-3G since mid 2006 has led to much improved NTFS support in Unix-like operating systems, considerably alleviating this concern. It is still not possible to use NTFS in DOS-like operating systems without third-party drivers, which in turn makes it difficult to use a DOS floppy for recovery purposes. Microsoft provided a recovery console to work around this issue, but for security reasons it severely limited what could be done through the Recovery Console by default. The movement of recovery utilities to boot CDs based on BartPE or Linux (with NTFS-3G) is finally eroding this drawback.

Due to its long history of usage on desktops and portable computers meanwhile spanning over more than three decades and its frequent use in embedded solutions, the FAT file system continues to be the most widespread file system worldwide.

NTFS (New Technology File System) is the standard file system of Windows NT, including Windows 2000, Windows XP, and all their successors to date.

NTFS supersedes the FAT file system as the preferred file system for Microsoft’s Windows operating systems. NTFS has several improvements over FAT and HPFS (High Performance File System) such as improved support for metadata and the use of advanced data structures to improve performance, reliability, and disk space utilization, plus additional extensions such as security access control lists(ACL) and file system journaling.

In the mid 1980s, Microsoft and IBM formed a joint project to create the next generation of graphical operating system. The result of the project was OS/2, but Microsoft and IBM disagreed on many important issues and eventually separated. OS/2 remained an IBM project. Microsoft started to work on Windows NT. The OS/2 file system HPFS contained several important new features. When Microsoft created their new operating system, they borrowed many of these concepts for NTFS.

The new features in Windows XP require on-disk data structures that make these volumes unavailable to Microsoft Windows NT 4.0-based computers. In anticipation of dual-boot scenarios, Microsoft recommends that you upgrade Windows NT 4.0 to Service Pack 4 (SP4) before you start the Windows XP installation. The version of NTFS included with Windows XP cannot be interpreted correctly by Windows NT 4.0. However, there is an updated Ntfs.sys driver in Windows NT 4.0 SP4 that enables Windows NT 4.0 to read from and write to NTFS volumes in Windows XP. Features of the NTFS 3.1 file system include:

·         Disk quotas: Administrators can limit the amount of disk space users can consume on a per-volume basis. The three quota levels are: Off, Tracking, and Enforced.

·         Encryption: The NTFS 3.1 file system can automatically encrypt and decrypt file data as it is read and written to the disk.

·         Reparse points: Programs can trap open operations against objects in the file system and run their own code before returning file data. This feature can be used to extend file system features such as mount points, which you can use to redirect data that is read and written from a folder to another volume or physical disk.

·         Sparse files: This feature permits programs to create very large files, but to consume disk space only as needed.

·         USN journal: This feature provides a persistent log of all changes made to files on the volume. This feature is one of the reasons that Windows domain controllers must use an NTFS 3.1 partition as the system volume.

NOTE:Microsoft Windows 2000 uses NTFS 3.0. NTFS 3.0 and 3.1 have compatible on-disk formats, so volumes upgraded to NTFS 3.1 by Windows XP can continue to be accessed by Windows 2000 or by Windows NT 4.0 with SP4 or later.