Serial Attached SCSI

Serial Attached SCSI (SAS) is a technology designed to move data to and from computer storage devices such as hard drives and tape drives. It is a point-to-point serial protocol that replaces the parallel SCSI. SCSI first appeared in the mid 1980s in corporate data centers. SAS uses the standard SCSI command set. At present it is slightly slower than the final parallel SCSI implementation, but in 2009 it will double its present speed to 6 Gbit/s. This will permit much higher speed data transfers. The protocol is "downwards"-compatible with second generation SATA drives. These drives may be connected to SAS backplanes (controllers), but SAS drives can not be connected to SATA backplanes. 
The SAS protocol is developed and maintained by the T10 technical committee of the International Committee for Information Technology Standards (INCITS) and promoted by the SCSI Trade Association (SCSITA).
Connectors.
The SAS connector is much smaller than traditional parallel SCSI connectors allowing for the small drives. SAS supports point data transfer speeds up to 3 Gbit/s, but is expected to reach 12 Gbit/s by the year 2012. 
The physical SAS connector is available in several different variants: