Memory system and method of operating the same

The memory system includes a memory controller and memory devices. The memory controller selectively operates the first command in one of a normal mode and a mixed mode of transmitting a mixture of the second command to the first command for continuously transmitted during a plurality of clock cycles. The memory device changes the command latch point according to the normal mode or the mix mode. Employing a mixing mode for transferring a mixture of the two commands in Kass-CAS delay time-to: it is possible to reduce the (tCCD CAS-to-CAS delay time). Kass-can prevent Kass DQ bubbles (bubble DQ) indicating a fail of the transfer of data is performed continuously through the phenomenon of reduced latency and increased utilization (utilization) of the data bus-to.