Small Computer System Interface (SCSI) was the most common interface used on legacy enterprise-class rotating hard drives. While traditional SCSI is a parallel interface, the trend in the storage industry is to serial these interfaces; thus were born Serial-Attached SCSI (SAS) and Serial ATA (SATA).
When the SCSI Trade Association introduced the SAS standard, it was designed to meet the ever-demanding needs of enterprise storage for high performance, high reliability and high manageability. SATA was designed to be the replacement drive interface for the high-volume desktop and mobile markets.
Both SATA and SAS use the same physical and electrical interface, and therefore, SATA drives can be physically connected to SAS host controllers. Because of additional command support, SATA host controllers will not support SAS devices. The three software protocols that can run on top of this interface are: Serial SCSI Protocol (SSP) - supports SAS drives, SATA Tunneling Protocol (STP) - supports SATA drives, Serial Management Protocol (SMP) - supports SAS expanders.
The SAS standard currently supports up to 3Gbit/sec data transfer speeds, with future rates planned for 6Gbit/sec and even 12Gbit/sec at the end of this decade.
Key end-user benefits of the standard include an enterprise-class command set, investment protection in compatible SCSI software and middleware, and the choice of direct-attach storage devices (SAS or SATA). In addition, longer cabling distances, smaller form factors and greater ease of device addressing will all lead to a new level of flexibility. Since SAS is based on the foundation of the industry-leading SCSI specification, it will satisfy users' needs for continuity in mission-critical applications.
SCSI is a parallel interface
