A serial-transmission type memory system with a hot swapping function is provided which is capable of replacing a defective memory module without stopping the system. One end of a row of memory modules is connected to one input-output section of a memory controller and the memory controller exerts control so that, when a failure occurs in any of the memory modules, by disconnecting the defective memory module from the memory module in its preceding stage and by sequentially connecting the memory module in the row of the memory modules in a next and onward stage and a spare memory module connected to another end of the row of the memory modules to the other input-output section of the memory controller in series through second read and write signal lines to gain access to each of the memory modules.
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