A computer system includes a system controller with a central processing unit and a memory bus controller operating in a first interface mode; a system memory connected with the system controller through the system bus; a NAND flash memory for storing a system driving code, an operating system program and user data for the computer system; and an interface unit communicating with the system controller through the system bus in the first interface mode and communicating with the NAND flash memory in a second interface mode, the interface unit being synchronized with a clock signal generated therein in response to predetermined command and operating information. The NAND flash memory may be used for the system bootstrap, and data transmission to the system controller during reading or programming operations is performed successively to reduce the latency time on the read operation and the data loading time on the programming operation.