SCSI, Fast SCSI, Ultra SCSI, Ultra2 SCSI: 8 devices
Wide SCSI, Fast Wide SCSI, Ultra Wide SCSI, Wide Ultra2 SCSI, Ultra3 SCSI, Ultra160 and 160+ and Ultra320 : 16 devices
Of course, the number of devices supported depends not only on protocol limitations, but cable length, number of cables used, etc.