SCSI, standing for Small Computer System Interface, is a parallel interface standard used primarily for high speed hard drives. It supports faster data transfer rates than the IDE storage interface. Since in this technology multiple SCSI hard drives can be connected to single SCSI interface, it is really an I/O bus rather than simply an interface.
Although SCSI has been popular in the past, today many users are switching over to SATA drives. SCSI is gradually evolved into SAS or serial attachment SCSI. SAS is a point-to-point serial interface in which controllers are linked directly to disk drives.