File System

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File system

File names
A file name is a name assigned to a file in order to secure storage location in the computer memory. Whether the file system has an underlying storage device or not, file systems typically have directories which associate file names with files, usually by connecting the file name to an index in a file allocation table of some sort, such as the FAT in a DOS file system, or an inode in a Unix-like file system. Directory structures may be flat, or allow hierarchies where directories may contain subdirectories. In some file systems, file names are structured, with special syntax for filename extensions and version numbers. In others, file names are simple strings, and per-file metadata is stored elsewhere. A file name is a name assigned to a file in order to secure storage location in the computer memory.By this file name a file can be further accessed Metadata

Other bookkeeping information is typically associated with each file within a file system. The length of the data contained in a file may be stored as the number of blocks allocated for the file or as an exact byte count. The time that the file was last modified may be stored as the file's timestamp. Some file systems also store the file creation time, the time it was last accessed, and the time that the file's meta-data was changed. (Note that many early PC operating systems did not keep track of file times.) Other information can include the file's device type (e.g., block, character, socket, subdirectory, etc.), its owner user-ID and group-ID, and its access permission settings (e.g., whether the file is read-only, executable, etc.). Arbitrary attributes can be associated on advanced file systems, such as XFS, ext2/ext3, some versions of UFS, and HFS+, using extended file attributes. This feature is implemented in the kernels of Linux, FreeBSD and Mac OS X operating systems, and allows metadata to be associated with the file at the file system level. This, for example, could be the author of a document, the character encoding of a plain-text document, or a checksum. Hierarchical file systems

The hierarchical file system was an early research interest of Dennis Ritchie of Unix fame; previous implementations were restricted to only a few levels, notably the IBM implementations, even of their early databases like IMS. After the success of Unix, Ritchie extended the file system concept to every object in his later operating system developments, such as Plan 9 and Inferno. Types of file systems

File system types can be classified into disk file systems, network file systems and special purpose file systems. Disk file systems
A disk file system is a file system designed for the storage of files on a data storage device, most commonly a disk drive, which might be directly or indirectly connected to the computer. Examples of disk file systems include FAT (FAT12, FAT16, FAT32, exFAT), NTFS, HFS and HFS+, HPFS, UFS, ext2, ext3, ext4, btrfs, ISO 9660, ODS-5,Veritas File System, ZFS and UDF. Some disk file systems are journaling file systems or versioning file systems. Flash file systems

A flash file system is a file system designed for storing files on flash memory devices. These are becoming more prevalent as the number of mobile devices are increasing, and the capacity of flash memories increase. While a disk file system can be used on a flash device, this is suboptimal for several reasons: * Erasing blocks: Flash memory blocks have to be explicitly erased before they can be rewritten. The time taken to erase blocks can be significant, thus it is beneficial to erase unused blocks while the device is idle. * Random access: Disk file systems are optimized to avoid disk seeks whenever possible, due to the high cost of seeking. Flash memory devices impose no seek latency. * Wear levelling: Flash memory devices tend to wear out when a single block is repeatedly overwritten; flash file systems are designed to spread out writes evenly. ....
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