Abstract: In a data processing system which is for use in combination with at least one peripheral device and comprises an input-output processor connected to a first and a second bus, a main memory connected to the first bus, a peripheral controller connected to the second bus and the peripheral device, and a central processor connected to the first bus and coupled to the second bus through the input-output processor, the peripheral controller requests data transfer between the main memory and the peripheral device. For this purpose, the peripheral controller produces a translation request signal in response to a channel command which is stored in a local memory of the peripheral controller from the main memory through the input-output processor and indicates the data transfer.