The interaction between the central processor and the peripheral devices. The devices report their status during data transfers so that the processor knows when an operation is completed and more data can betransferred.

• 中央处理机与外部设备之间的信息交换。在数据传送期间，这些外部设备向中央处理机报告它们的状态，以使中央处理机知道操作何时完成以及何时可以再传送数据。