题目:To transfer data from an I/O device to memory, the DMA controller first sends a ( ) to the CPU by setting BR to 1. 为了将数据从I/O设备传输到存储器,DMA控制器首先向CPU发送总线请求,将BR位设置为1。
A. data transfer
B. bus request
C. connection establish
D. bandwidth requirement
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