| 摘要 |
PURPOSE:To reduce the overhead by using a means which switches the 1st and 2nd means during a single input/output request and performing the transfer of data between an external memory device and an extended memory device via the 2nd means only to a specific command received during the single input/ output request. CONSTITUTION:A subchannel 4 contains a control bit 5 to transfer data to an extended memory device 15; while a subchannel 11 has a control bit 12 which does not transfer data to the device 15. When data are transferred between an external memory device 13 and a memory device with a prescribed specific command, a data transfer line 6 is used for transfer of data to the device 15. While a data transfer line 7 is used for the transfer of data to a main memory 16 with another command. Furthermore a data transfer line 9 is always used for transfer of data to the memory 16 when data are transferred between a memory device and an external memory device 14 connected to the subchannel 11.
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