NAS is one of the three main storage architectures. The other two are storage area networks (SAN) and direct-attached storage (DAS):
Storage area networks
A storage area network (SAN) provides block storage to networked devices. Each block is formatted with different protocols. For example, one block can be formatted for NFS, and another can be formatted for AFP.
NAS vs. SAN
The main difference between NAS and SAN is the way client machines view the storage device. To clients, NAS works as a file system and SAN works as the operating system. NAS handles individual file requests, but SAN manages requests for contiguous blocks of data. NAS and SAN also use different underlying protocols and technologies.
SAN is more flexible for users, but it can cost more to set up and manage.
Direct-attached storage
Direct-attached storage (DAS) is storage that can be directly attached to a single computer. The most common example of DAS is a cable-connected external hard drive. For another computer to access files on that drive, the cable must be removed from the original computer and attached to the new one.
NAS vs. DAS
DAS was the precursor to NAS. DAS performs better than NAS, especially for software programs that require more computing. However, being directly attached, it does not lend itself well to sharing and is complex to manage.