Two legacy direct attached storage (DAS) interconnects are commonly used in SAN and NAS products:
The parallel SCSI bus, which began its history as part of the same technology as SCSI logic and protocols, is the leading interconnect for server systems and UNIX desktops. It has excellent performance characteristics and a great deal of versatility to support a wide range of functions and devices. Parallel SCSI is relatively expensive compared to ATA.
ATA was invented as an inexpensive disk interconnect for PC desktop computers. It is much more limited than parallel SCSI in both expandability and device support, but the cost of ATA technology is lower than any other storage interconnect technology.