1. A data processing method for randomly accessing memory of a semiconductor disk device, the method comprising: in response to a random access command, setting information in a register to select data that is to be accessed; determining whether the random access command corresponds to a first random access type or to a second random access type that is different than the first random access type; in response to the random access command corresponding to the first random access type, accessing data in a first unit of a first memory of the semiconductor disk device to provide an accessed result and partly masking the accessed result using the information that was set in the register; and in response to the random access command corresponding to the second random access type, successively conducting a random access operation in a second unit of the first memory, which is smaller than the first unit using the information that was set in the register.