Direct-attached storage (DAS) is digital storage directly attached to the computer accessing it, as opposed to storage accessed over a computer network (i.e. network-attached storage). Examples of DAS include hard drives, solid-state drives, optical disc drives, and storage on external drives. The name “DAS” is a retronym to contrast with storage area network (SAN) and network-attached storage (NAS).
A typical DAS system is made of a data storage device (for example enclosures holding a number of hard disk drives) connected directly to a computer through a host bus adapter (HBA). Between those two points there is no network device (like hub, switch, or router), and this is the main characteristic of DAS.
The main protocols used for DAS connections are ATA, SATA, eSATA, NVMe, SCSI, SAS, USB, USB 3.0, IEEE 1394 and Fibre Channel.