Without the tristate gate, it would be almost impossible to design a modern computer. Why is this so?

What will be an ideal response?

Tristate gates are used to allow one of several devices to put data onto a common bus. A tristate device has three output states: high (driving the bus), low (driving the bus), and high?impedance (disconnected from the bus). The tristate gate makes it easy to design bused systems. The output of any tri?state device connected to a bus has tristate control logic. This allows one and only one device connected to a bus to drive the bus. All other devices connected to the bus are disconnected electrically by assuming the third state.

Without tristate gates you would have to drive buses with an alternative technology (e.g., open?collector or open?drain circuits). However, these are very similar to tristate logic in the sense that they allow one out of n devices to drive the bus.

If there were no tristate drives (or open?collector/open?drain) the only other way that a buses system would be possible would be to use multiplexers to control buses. This would be a rather cumbersome solution.