Solution

The correct answer is (A), (C), (B), (D).

Key Points

• Initiate DMA transfer request: The first step in a DMA transfer is to initiate the request. This is done by the peripheral device that needs to transfer data directly to or from the memory.
• Processor grants DMA control over the system bus: Once the DMA request is initiated, the processor needs to grant control of the system bus to the DMA controller. This allows the DMA controller to directly access the memory without the intervention of the processor.
• Transfer data directly between peripheral and memory: With control over the system bus, the DMA controller can then transfer data directly between the peripheral device and the memory, bypassing the CPU.
• DMA controller completes data transfer and signals completion: After the data transfer is complete, the DMA controller will signal the completion of the transfer, allowing the processor to regain control of the system bus.

Thus the correct answer is ​(A), (C), (B), (D).

Additional Information

• Direct Memory Access (DMA) is a feature that allows peripherals to communicate directly with the system memory, bypassing the CPU to speed up memory operations and free up CPU resources for other tasks.
• DMA is commonly used in scenarios where large amounts of data need to be transferred quickly, such as in disk operations, audio and video streaming, and network data transfer.
• By offloading data transfer tasks to the DMA controller, the overall system performance can be significantly improved, especially in I/O-bound applications.