Basically, a network-attached storage  (NAS) device is a small computer with an Internet connection, with one or more hard drive bays, and usually run on Linux-based operating system. NAS are a must for peopel with large media libraries, and when Dropbox or Google aren't enough, but want access to all thuis data over the internet anywhere. Your oen 'cloud'.

Businesses use advanced versions of NAS, with iSCSI targeting, SANs (storage area networks), or RAID configurations such as RAID 5, 6, or 10 for multidrive NAS devices.

The best NAS for most home users: QNAP Turbo NAS TS-251 (Easy to set up and manage, great data protection, media streaming, remote access, and lots of add-on apps.)

The second best NAS for most home users: Synology DiskStation DS214 (without disks) (Only 512 MB memory, less powerful processor, also costs less than QNAP model)

The best NAS for most home users with easy setup and file management: WD My Cloud Mirror (with two 2TB drives): The best option for normal users, very user-freindly