File management in UNIX and windows 2000 File Management system is that set of system software that provides services to users and applications in the use of files. The only way that a user or application may access files is through the file management system. This relieves the user or programmer of the necessity of developing special-purpose software for each application .

UNIX File Management UNIX file system is hierarchical file system. The directory that you are placed when you first log on to the system is called the home directory. System administrator creates the home directory for each user.

Different Type Of Files Ordinary files Directories Special files Pipes

Ordinary Files This type of file is used to store information, such as some text or an image. Any file is always contained within a directory. Files do not actually reside inside directories. A directory is a file that contains references to other files. The directory holds two pieces of information about each file:  Its filename. An inode number which acts as a pointer to where the system can find the information it needs about this file.

Directories A directory is a file that holds other files and other directories. You can create directories in your home directory to hold files and other sub-directories. Having your own directory structure gives you a definable place to work from and allows you to structure your information in a way that makes best sense to you.  

Special Files This type of file is used to represent a real physical device such as a printer, tape drive or terminal. It may seem unusual to think of a physical device as a file, but it allows you to send the output of a command to a device in the same way that you send it to a file.

Pipes UNIX allows you to link commands together using a pipe. The pipe acts a temporary file which only exists to hold data from one command until it is read by another. The pipe takes the standard output from one command and uses it as the standard input to another command  

Structure Of The File System. The UNIX file system is organized as a hierarchy of directories starting from a single directory called root which is represented by a / (slash). Imagine it as being similar to the root system of a plant or as an inverted tree structure. Immediately below the root directory are several system directories that contain information required by the operating system.  

Controlling Access To Files And Directories Every file and directory in your account can be protected from or made accessible to other users by changing its access permissions. You can only change the permissions for files and directories that you own  

Controlling Access To Files And Directories(contd.) The user has following options Displaying access permissions Understanding access permissions Default access permissions Changing group ownership of files and directories Changing access permissions

i-node A Unix file is described by an information block called an i-node. There is an i-node on disc for every file on the disc and there is also a copy in kernel memory for every open file. All the information about a file, other than it's name, is stored in the i-node

i-node(contd.) The following information is contained in the i-node File access and type information, collectively known as the mode. File ownership information. Time stamps for last modification, last access and last mode modification. Link count. File size in bytes. Addresses of physical blocks.

Structure of i-node

Structure of the i-node(contd.) There are 13 physical block addresses in an i-node, each of these addresses is 3 bytes long. The first ten block addresses refer directly to data blocks, the next refers to a first level index block the next refers to a second level index block which holds the addresses of further index blocks the last refers to a third level index block which holds the addresses of further second level index blocks.

Windows 2000 File System   Windows 2000 supports a number of file systems, including the file allocation table (FAT) that runs on windows 95, MS DOS, and OS/2. But the developers of windows 2000 also designed a new and a very effective file system, NTFS file system

NTFS Physical Structure The NTFS partition theoretically can be almost of any size NTFS divides all useful place into clusters - data blocks used at a time. NTFS supports almost all sizes of clusters - from 512 bytes up to 64 KBytes. The 4 KBytes cluster is considered to be some standard..

NTFS Layout

Overview Of Partition structure NTFS disk is symbolically divided into two parts The first 12% of the disk are assigned to so-called MFT area (Master File Table). The MFT-area is always kept empty not to let the most important service file (MFT) be fragmented at growth. The rest 88% of the disks represent usual space for files storage.

MFT & Its Structure The most important file on NTFS is named MFT or Master File Table - the common table of files MFT is divided into records of the fixed size (usually 1 KBytes), and each record corresponds to some file. The first 16 files are housekeeping and they are inaccessible to the operating system. They are named metafiles and the very first metafile is MTF itself.

Features Of NTFS Directories Journalizing Compression Security Encryption Recoverability      

Directories The directory on NTFS is a specific file storing the references to other files and directories establishing the hierarchical constitution of disk data The directory file is divided into blocks, each of them contains a file name, base attributes and reference to the element MFT which already gives the complete information on an element of the directory.

Journalizing NTFS is a fail-safe system which can correct itself at practically any real failure. NTFS just doesn't have intermediate (erratic or incorrect) conditions - the data variation quantum cannot be divided on before failure or after it bringing breakups and muddle - it is either accomplished or cancelled.  

Compression Files on the NTFS volume have one rather useful attribute - "compressed". Any file or directory in the individual order can be stored on the disk in the compressed form and this process is completely clear for applications The file compression has very much high speed and only one large negative property - huge virtual fragmentation of compressed files which however does not bother anybody.

Security NTFS is supposed to be the most perfect file system from all nowadays existing. In theory it is undoubtedly so, but in current implementations unfortunately the rights system is far enough from the ideal. NTFS file system rights are close connected with the system itself, and that means they are not obligatory to be kept by another system if it is given physical access to the disk

Encryption Each file or directory can be encrypted and thus cannot be read by another NT installation. In combination with standard and safe password on the system, important data selected by you can be protected.

Recoverability Each file on an NTFS volume is listed as a record in a special file called the Master File Table (MFT). The first record in the table describes the MFT itself. second record is an MFT "mirror" record. If the first MFT record is corrupted, NTFS uses the second record to find the MFT mirror file. The third record in the MFT is the log file which records all file transaction information.

Recoverability(contd.) If a transaction completes successfully, NTFS commits the file update to disk. If the transaction is not complete, NTFS ends or rolls back the transaction. If the system crashes, NTFS performs three passes through the data on the disk: an analysis pass, a redo pass, and an undo pass.

Recoverability(contd.) The NTFS recovery pass involves the following six steps: When Windows NT recognizes an NTFS volume, it reads the MFT. NTFS calls the Log File Service to open the log file. This causes the Log File Service Recovery to take place. NTFS calls the Log File Service to read its restart area and reads all the data from the last checkpoint operation. This data initializes the transaction table, dirty pages table, and open file table so they can be used in the recovery process. NTFS performs an analysis pass on its last checkpoint record. At the end of this pass, the transaction table contains only transactions that were active when the 5. NTFS performs a redo pass. At the end of this pass, the cache reflects the state of the volume when the crash occurred. 6. NTFS performs an undo pass. At the end of this pass, the volume is recovered to a stable state

Advantages Of NTFS The NTFS file system is best for use on volumes of about 400 MB or more, because performance does not degrade as much on larger NTFS volumes as compared to larger FAT volumes You can assign permissions to individual files and folders, so you can specify who is allowed various kinds of access to a file or folder