File System

A file system is a persistent Data structure used to efficiently store, retrieve, and manage files. Most file systems are proprietary and specific to a particular operating system, but some are defined in ISO standards and used for independent data interchange between systems. Examples of proprietary file systems are NTFS (used by Windows) and ODS (used by OpenVMS). Examples of non-proprietary systems are FAT and FAT32 (the most common for USB thumbdrives), and exFat.

Because file systems are typically used on block-oriented devices (like hard disks), they are optimized for use on such. One such optimization is the ability to store files in discontiguous segments, called extents, which is both faster for resizing files, and makes efficient use of the fixed space on such devices. Over time, these file extents become scattered across the device, which can result in slower file access (and may significantly slow the operating system as well) due to the seek and latency times inherent in mechanical devices. The use of defragmenting software was necessary to collect the extents together and make the file system operate faster. Most modern systems use other methods to keep the file systems defragmented, and modern storage devices (such as SSDs, which do not possess mechanical access mechanisms) are less subject to slowness due to fragmentation.

## Features[edit]

Most file systems provide a common set of features.

* Create new files
* Delete files and release their space for reuse
* Resize files
* Read and write file
* Read and write file meta data (file name, flags, access dates, etc.)
* Directories (aka folders)
* Search for files using wildcard expressions