A NAS unit is essentially a self-contained computer connected to a network, with the sole purpose of supplying file-based data storage services to other devices on the network.
The operating system and other software on the NAS unit provide the functionality of data storage, file systems, and access to files, and the management of these functionalities.
The unit is not designed to carry out general-purpose computing tasks, although it may technically be possible to run other software on it. NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often by connecting a browser to their network address.
The alternative to NAS storage on a network is to use a computer as a file server. In its most basic form a dedicated file server is no more than a NAS unit with keyboard and display and an operating system which, while optimised for providing storage services, can run other tasks; however, file servers are increasingly used to supply other functionality, such as supplying database services, email services, and so on.
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