NTFS - The NT File System is an advanced file system used in Windows NT. NTFS is not available for Windows 95 because it would require a massive real mode MSDOS driver to support an NTFS boot drive or NTFS access from MSDOS mode.

NTFS uses cluster sizes of 512, 1024, 2048 or 4096 bytes. Larger sizes up to 64K bytes can be used optionally. Presumably the maximum disk size is constrained by the Master Boot Record -- which is required for compatibility with other OSes. The limit with 512 byte sectors used on PC hard drives would be 2 Terabytes.

NTFS differs from FAT16 and FAT32 in that the separate directory, FAT and file structures are merged into a single structure called the Master File Table. The MFT consists of 16 records of general data followed by one record for each file on the disk. Directories are files whose data is a list of indices to other files. Large directories are organized as data structures called B-Trees that allow rapid updating and accessing. The resident record for each file contains attributes and will be linked to additional storage if all the attributes can not fit into one record. The file contents (data) are just one of the attributes. Attributes include file names, access control, security information file size, etc. Some attributes -- primarily those inherited from FAT -- are global. Others -- such as security -- are user specific. The data attribute for short files may be stored in the resident record and may not require additional storage.

Specific capabilities of NTFS include all FAT capabilities (System, hidden, read-only, archive attributes, time tags, file size 8.3 file names). NTFS also supports security, 255 Unicode character file names, POSIX (Unix) required file system capabilities, file compression, and multiple named file streams.

File updating in NTFS requires updating a log area in the MFT and of the data. This is claimed to be substantially faster than FAT. Upon boot the Log area is checked against actual disk contents and any incomplete transactions are backed out. This is much faster than disk recovery in either FAT or write optimized file systems such as hpfs or Unix. NTFS is claimed to be proof against all software induced disk failures and -- with mirroring -- against all single point hardware failures. NTFS files can become fragmented, but are purportedly less prone to do so than FAT files.

Web References:

http://www.melbpc.org.au/pcupdate/9605/wntfs.htm http://www.microsoft.com/salesinfo/qa/qa5889.htm http://premium.microsoft.com/support/ntserver/serviceware/06904827.asp http://www.microsoft.com/ntworkstation/info/ntwreskit.htm http://technet.microsoft.com/en-us/library/cc788654.aspx

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