EXTERNAL MEMORY CONTROLLER

PURPOSE:To guarantee the compatibility of data when an external storage device is abnormality stopped by the fault of a compressing/extending mechanism or the like by reducing the burden of the software of a host device for retrial and writing a data pattern, which can not be compressed, without any compression processing. CONSTITUTION:When the compression processing is instructed, data sent from a host device 2 are compressed by a compressing/extending mechanism 6 and transferred to a data buffer 8 later. In this case, when any fault is detected by a hardware fault detecting mechanism 10 or a data pattern fault detecting mechanism 11, a microprocessor 5 instructs the retransfer of the transferred data. The retransferred data are not compressed by the compressing/extending mechanism 6 but directly transferred through a data buffer control part 9 to the data buffer 8 and further retried through a recording/reproducing mechanism control part 7 to an external storage device 3. Thus, the software burden of the host device 2 is reduced, and the compatibility of data is guaranteed.