Operating Systems question: Direct memory access is used for high-speed I/O devices in order to avoid increasing the CPU

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Operating Systems question:
Direct memory access is used for high-speed I/O devices in order
to avoid increasing the CPU’s execution load.
a. How does the CPU interface with the device to coordinate the
transfer?
b. How does the CPU know when the memory operations are
complete?
c. The CPU is allowed to execute other programs while the DMA
controller is transferring data. Does this process interfere with
the execution of the user programs? If so, describe what forms of
interference are caused.