SCSI or Small Computer System Interface was initially designed to be by computers for small data transfer. However, it has been upgraded to support data transfer up to 320 Megabytes per second. SCSI is a pretty fast interface that can be used to transfer data to different devices that are connected to a computer at the same time.
However, as fast as SCSI is, one of the limitations it has is that it can only be used independently by computers due to the fact that the BOIS system support in it is quite limited in capacity. On the other hand, SAS or Serial Attached SCSI was designed to improve on all the limitations of SCSI.
The fact that SAS is a serial interface is the reason why it can efficiently control all the drives that are attached to it. SAS is equipped with the capacity to accommodate up to 128 different drives at a time.