SAS is a performance improvement over traditional SCSI because SAS enables multiple devices (up to 128) of different sizes and types to be connected simultaneously with thinner and longer cables; its full-duplex signal transmission supports 3.0Gb/s. In addition, SAS drives can be hot-plugged.Serial Attached SCSI (SAS) is a data transfer 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 bus technology that first appeared in the mid 1980s in corporate data centers, and 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, allowing for much higher speed data transfers than previously available, and is "downwards"-compatible with second generation SATA drives. SATA 3.0 Gbit/s drives may be connected to SAS backplanes, but SAS drives may 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).