Small Computer System Interface or SCSI (SCASI), in electronics and computer science, is a standard interface designed to perform parallel data transfer on bus. To connect a computer to a host, the connection bus needs a SCSI host adapter that handles data transfer on the bus itself. The device must have a SCSI controller, which is usually built into all peripheral devices, with the exception of older ones. The SCSI interface is mostly used for communication with hard disk drives and mass storage tape drives, but also for connecting a wide range of devices, such as image scanners, CD readers and writers (CD-R and CD-RW), DVD players. In fact, the SCSI standard has been designed to promote the interchangeability and compatibility of devices (all, at least in theory). There are also SCSI printers.