A computer chip set is devised for use on a computer mother board with at least two clock rates including a first clock rate and a second clock rate for the purpose of converting an input signal referencing either the first or second clock rate to an output signal referencing the other clock rate. The first and second clock rates are in virtual synchronism and have a fixed ratio between them. The computer chip set utilizes a phase signal generator capable of generating a set of phase signals and a signal conversion logic circuit for generating the output signal referencing one of the first and second clock rates other than the one referenced by the input signal. This computer chip set can allow the computer mother board to be operated without waiting a state so that the data processing efficiency of the computer mother board can be enhanced. A multiplexer means used in the computer chip set of the invention has an output which is selectively muliplexed between the first clock rate and the second clock rate to serve as a third clock signal. This computer chip set allows the designer to use a slower clock rate to drive the DRAM.