For Ultra 450 systems, there are two internal SCSI busses. The device "scsi" refers to the internal SCSI I/O bus for internal disks, while device "scsix" refers to the removeable-media and external (connector on back panel) internal SCSI bus.
The following shows the output of a devalias command on a Sun Ultra 450 UPA/PCI system.
ok devalias screen /SUNW,ffb@1d,0 disk /pci@1f,4000/scsi@3/disk@0,0 disk0 /pci@1f,4000/scsi@3/disk@0,0 disk1 /pci@1f,4000/scsi@3/disk@1,0 disk2 /pci@1f,4000/scsi@3/disk@2,0 disk3 /pci@1f,4000/scsi@3/disk@3,0 scsi /pci@1f,4000/scsi@3 diskx0 /pci@1f,4000/scsi@2/disk@0, diskx1 /pci@1f,4000/scsi@2/disk@1,0 diskx2 /pci@1f,4000/scsi@2/disk@2,0 diskx3 /pci@1f,4000/scsi@2/disk@3,0 cdrom /pci@1f,4000/scsi@2/disk@6,0:f tape /pci@1f,4000/scsi@2/tape@4,0 scsix /pci@1f,4000/scsi@2 pci /pci@1f,4000 pcia /pci@1f,2000 pcib /pci@1f,4000 pci0 /pci@1f,4000 pci1 /pci@1f,2000 pci2 /pci@4,4000 pci3 /pci@4,2000 pci4 /pci@6,4000 pci5 /pci@6,2000 flash /pci@1f,4000/ebus@1/flashprom@10,0 nvram /pci@1f,4000/ebus@1/eeprom@14,0 parallel /pci@1f,4000/ebus@1/ecpp@14,3043bc net /pci@1f,4000/network@1,1 ebus /pci@1f,4000/ebus@1 i2c /pci@1f,4000/ebus@1/SUNW,envctrl floppy /pci@1f,4000/ebus@1/fdthree tty /pci@1f,4000/ebus@1/se ttyb /pci@1f,4000/ebus@1/se:b ttya /pci@1f,4000/ebus@1/se:a keyboard! /pci@1f,4000/ebus@1/su@14,3083f8:forcemode keyboard /pci@1f,4000/ebus@1/su@14,3083f8 mouse /pci@1f,4000/ebus@1/su@14,3062f8