Discussion
Which of the following task is performed by Direct Memory Access (DMA) in a computer system ?
Answer: B
DMA allows data transfer between a storage unit and main memory independent of the CPU.
A DMA controller takes over the system buses (the CPU grants them in response to a bus request) and moves a block of data directly between an I/O device and memory. The CPU only initialises the transfer and is interrupted when it ends, so it is free during the transfer.
Transfers under CPU control are programmed or interrupt-driven I/O, which DMA replaces. DMA does not bypass memory to talk to the CPU, and transfers between the CPU and memory are ordinary memory access, not DMA.
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