What is required for NAS?

Background: I am interested in having shared storage accessible to all computers coected to the network. Primarily I’m focusing on SOHO.

Question: It appears NAS requires a hard disk enclosure, which takes the disks and facilitates the network coection. Does any hard disk work, or do they need to be special for NAS? There seems to be several hd marketed for NAS but is this anything special or just a marketing gimmick?