A file-level storage system known as Network Attached Storage (NAS) uses one or more servers with dedicated disks to store and distribute data to several clients connected to a network. Along with storage area networks (SAN) and direct-attached storage (DAS), NAS is one of the three primary storage designs. It is the only one that is both intrinsically networked and entirely in charge of the storage of an entire network.

Contrast NAS with more recognizable storage volumes, such as the USB flash drive, CD, external drive, or hard drive on your PC. Like any storage volume, file-based data can be stored and shared using a NAS architecture. NAS is networked to handle multiple devices at once, but your hard disk, external drive, CD, or flash drive can only connect to one device at a time.

The purpose of network-attached storage systems is to store data as files. NAS machines run software that manages rights and safeguards data, but they can also technically perform typical server functions. Because of this, NAS devices do not require a fully functional operating system. The majority of NAS devices come with a lightweight, embedded operating system that has been optimized for data presentation and storage.

The Network File System (NFS), Server Message Block (SMB), Common Internet File System (CIFS), and/or Apple Filing Protocol (AFP) are common file-based protocols that a NAS unit uses to display these files. These protocols are used to communicate with Linux® and UNIX, Microsoft Windows, and Apple devices, respectively.