Definition of a File System

A file system is an abstract concept that is used to describe how the operating system kernel handles certain operating system functions related to the storage and retreival of information. Information is stored and accessed by the kernel and the user as if all information and system components are part of one large hierarchichal storage system, even though the information might be stored in different formats or use different Applicaiton Programming Interfaces (API) to store and retreive the data. Examples of what can be included in the file system are: devices such as network cards, serial ports; storage devices such as hard disks, CD-ROMs and DVDs, system and user processes, temporary data and even computer programs and user data files.

  • The '/' character represents the root of the filesystem
  • All other 'file systems' are mounted (attached) to this root or somewhere below it.
  • All file systems store and organize the data in a hierarchichal fashion
  • Some file systems are kernel constructs (PROCFS is a good example)
  • Some file systems are tied to actual storage devices.

Filesystem Types

  • Common File Systems (System V UNIX, BSD, Solaris, Linux)
    • EXT2/EXT3 - Linux disk-based file system
    • UFS
    • CD-ROM file systems
      • High Sierra File System (HSFS)
      • ISO 9660
      • UDF (DVDs)
    • NFS
    • PROCFS
    • TMPFS
    • swap
  • Other UNIX File Systems
    • HP-UX - Veritas VxVM, VxFS
    • Tru64 - ADVFS
    • AIX - JFS

The Common Filesystems

UNIX uses several types of file systems for different purposes.

Second Extended File system.
Third Extended File system. This is the most common Linux disk-based file system in Red Hat and some other operating systems, though not the only file system Linux systems can use. EXT3 provides improvements in availability, data integrity and speed over EXT2 file systems by implementing an improved journalling mechanism and using atomicity and consistency to guarantee file system consistency and availability. EXT3 is backwards and forwards compatible with EXT2 file systems. The EXT3 file system can operate in three modes: writeback, ordered (the default) and journal.
The UNIX File System, the most common disk-based file system for information storage and retreival on UNIX based computers.
High Sierra File System - Used for reading CD-ROMs
Network File System - Used for sharing disk information across the network.
Process File System - Used on UNIX, BSD and Linux for all processes currently running on the system. The filesystem is usually mounted as /proc.
Temporary File System - Solaris and most System V UNIX systems store data in /tmp and erase /tmp when the computer shuts down.

Other File Systems

  • VxFS - HP-UX - Veritas File System, a filesystem used by HP-UX but patented/owned by Veritas. (Update: Veritas is now owned by Symantec)
  • ADVFS - True64
  • JFS - AIX



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