The present invention is to provide a computer for
backup and being fault-tolerant comprising a CPU connected to an I / O port, a dual-port memory, a
memory address decoder, a
bus tri-state buffer, and an arbitration circuit, where the CPU can access data of the dual-port memory based on a decoded
memory address of the
memory address decoder, first and second ports of the dual-port memory are connected to input and output of the
bus tri-state buffer respectively, and an output of the arbitration circuit is connected to an enable terminal of the
bus tri-state buffer. Thus, when two identical computers are connected together as a dual computer
system, both computers can perform the same operations, compare and change operation data each other via the I / O port and the dual-port memory, and control an output value of the arbitration circuit based on the comparison results for causing the bus tri-state buffer to enter a bi-directional communication state or a
high impedance disconnected state, forcing either malfunctioned computer to surrender its control of the
system bus.