Why tri-state device is useful in bus oriented system?

In a multiplexed bus system, many devices are connected to

a common bus. If 2 or more devices attempt to use the bus

at the same time , then data will be lost. Thus only one

one device must be allowed to use the bus at a time. One

method is to connect the devices through tri-state

devices , which when disabled will effectively disconnect

devices from the bus.