An ongoing standardisation effort to extend the capabilities of SCSI-2. SCSI-3's goals are more devices on a bus (up to 32); faster data transfer; greater distances between devices (longer cables); more device classes and command sets; structured documentation; and a structured protocol model. In SCSI-2, data transmission is parallel (8, 16 or 32 bit wide). This gets increasingly difficult with higher data rates and longer cables because of varying signal delays on different wires. Furthermore, wiring cost and drive power increases with wider data words and higher speed.