The VAX-11/780 uses the Unibus and Massbus for I/O. Unibus is used for attaching lower-speed peripherals such as terminals and printers and Massbus for higher-speed disk and tape drives. Both buses are provided by adapters that interface the bus to the SBI. All systems come with one Unibus as standard, with up to four supported. Massbus is optional, with up to four supported. The VAX-11/780 also supports Computer Interconnect (CI), a proprietary network to attach disk drives and potentially share them with other VAX computers. Later, this feature was used to connect VAX computers in a VMScluster.