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File System And Features Of UNIX Operating System

FILE SYSTEM

A file is an object on a computer that stores data, information, settings, or commands that are used with a computer program. All of the files in the UNIX file system are organized into a multi-leveled hierarchy called a directory tree.

UNIX File System is organized in tree structure.

File tree can be arbitrarily deep. 

File name must not longer than 256 characters.

Single path name must not longer than 1023 characters.

  • ORDINARY OR REGULAR FILES
    A large majority of the files found on UNIX and Linux systems are ordinary files. Ordinary files contain ASCII (human-readable) text, executable program binaries, program data, and more.

  • DIRECTORIES
    A directory is a binary file used to track and locate other files and directories. The binary format is used so that directories containing large numbers of filenames can be search quickly.

  • DEVICE (SPECIAL) FILES
    Device or special files are used for device I/O on UNIX and Linux systems. They appear in a file system just like an ordinary file or a directory. On UNIX systems there are two flavors of special files for each device, character special files and block special files. Linux systems only provide one special file for each device. When a character special file is used for device I/O, data is transferred one character at a time. This type of access is called raw device access. When a block special file is used for device I/O, data is transferred in large fixed-size blocks. This type of access is called block device access. 

FEATURES OF UNIX

  • MULTI USER CAPABILITY
    In multi user system all users share various computer resources (hard disk, printer, and memory).

  • MULTI TASKING CAPABILITY
    It is capable of carrying out more than one job at the same time. It allows user to type in a program in its editor while it simultaneously executes some other commands like sort, copy a huge file. The later job is performed in the background while in the foreground uses the editor or takes a directory listing or anything else. This is managed by dividing  the  CPU  time  intelligently between all process being carried out. Depending on the  priority of the task, the OS approximately allots small time slots (of  the order of milliseconds or microseconds) to each foreground and background task.

  • COMMUNICATION
    The communication may be within the network of a single main computer or between two or more such computer networks. The users can easily exchange mail, data programs    through   such networks. Distance posses no barrier to passing information or messages to and from.

  • SECURITY
    Unix has 3 inherent provisions for protecting data.
    i) Assign passwords and login name to users area.
    ii) Provide read, write and execute permission to each file.
    iii) Encrypt files into an unreadable format, and decrypting the file is also possible.

  • PORTABILITY
    Unix is a highly portable OS. It can be ported to a variety of hardware platforms. It is the only system which has been ported across various hardware platforms of major vendors such as IBM, DEC, HP and SUN. Most OS is written for one specific machine or platform only.

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