A file server is a computer attached to a network, most often a local area network (LAN), whose primary function is to serve as centralized data storage for multiple machines as part of the client-server model of computer networking. They are available in a number of different hardware and software configurations. File servers are sometimes used to backup critical data. A typical file server will be configured only to send and receive files, and will not run any active processes for users. They may also be configured to distribute data over the Internet using FTP (file transfer protocol) or HTTP (hypertext transfer protocol).
Any modern computer may be configured to serve as a file server. A simple personal computer sharing music files throughout a home network is functioning as a file server. In larger organizations, file servers are generally dedicated computers, most often equipped with arrays of very large storage devices. The most specialized form of file server in common use in a modern computing scheme consists of computers that are designed specifically to serve only as file servers. These dedicated devices provide network-attached storage (NAS) using hardware that is generally configured to maximize only their performance in storing and sharing data and includes only very basic input/output and processing capabilities.
File servers can operate using either standard or specialized operating systems. All modern operating systems are designed to allow computers to serve as file servers. The Linux operating system enjoys considerable popularity on file servers both because of its reputation for stability and for economic reasons. Windows® and UNIX® are also frequently used as file server operating systems. NAS units may employ versions of standard operating systems but may also use specialized limited-function operating systems.
File servers are commonly encountered in situations where sharing data is beneficial. Large networks employ file servers to facilitate the sharing of data between users. Network systems that employ centralized file servers are also easier to secure because all files are located on centrally-located hardware and can be more easily backed up.
All file servers will occasionally experience performance degradation when demand for data is particularly high, but servers attached to the Internet are also vulnerable to attack. Denial-of-service or distributed denial-of-service (DoS or DDoS) attacks have frequently been used against file servers connected to the Internet. In each case, attackers flood a file server with so many malicious requests for data that legitimate requests are frequently lost or experience unacceptable delays.