计算机运行过程中，CPU需要与外设进行数据交换。采用（ ）控制技术时，CPU与外设可并行工作。
- A.程序查询方式和中断方式
- B.中断方式和DMA方式
- C.程序查询方式和DMA方式
- D.程序查询方式、中断方式和DMA方式
正确答案及解析
正确答案
解析
程序控制（查询）方式：CPU需要不断查询I/O是否完成，因此一直占用CPU。
程序中断方式：与程序控制方式相比，中断方式因为CPU无需等待而提高了传输请求的响应速度。
DMA方式：DMA方式是为了在主存与外设之间实现高速、批量数据交换而设置的。DMA方式比程序控制方式与中断方式都高效。CPU只负责初始化，不参与具体传输过程。
本题DMA和程序中断方式，是可以让外设与CPU并行的。
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