Network-attached storage (NAS) is file-level computer data storage connected to a computer network providing data access to aheterogeneous group of clients. NAS not only operates as a file server, but is specialized for this task either by its hardware, software, or configuration of those elements. NAS is often manufactured as a computer appliance – a specialized computer built from the ground up for storing and serving files – rather than simply a general purpose computer being used for the role.^{[nb 1]}

As of 2010 NAS devices are gaining popularity, as a convenient method of sharing files among multiple computers.^[1] Potential benefits of network-attached storage, compared to file servers, include faster data access, easier administration, and simple configuration.^[2]

NAS systems are networked appliances which contain one or more hard drives, often arranged into logical, redundant storage containers or RAID. Network-attached storage removes the responsibility of file serving from other servers on the network. They typically provide access to files using network file sharing protocols such as NFS, SMB/CIFS, or AFP.

Note that hard drives with "NAS" in their name are functionally the same as other drives. For example, an NAS SATA hard disk drive can be used as an internal PC hard drive, without any problems or adjustments needed. Here, NAS simply indicates a higher quality standard than consumer drives, which is why they usually quote MTBF figures (and are more expensive). Likewise, "Enterprise" drives are an even higher level of quality (and price).