What role does the DMA controller play in the process of data transfer between…
2025
What role does the DMA controller play in the process of data transfer between peripheral devices and main memory?
- A.
It bypasses the CPU and transfers data directly between memory and devices.
- B.
It uses the CPU's ALU for performing all transfers.
- C.
It interrupts the CPU to process each byte individually.
- D.
It sends data to the CPU first before writing to memory.
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Show answer & explanation
Correct answer: A
In computer architecture, when a high-speed peripheral device (like a hard drive, solid-state drive, or network interface card) needs to move massive amounts of data into RAM, traditional CPU-managed methods become an enormous bottleneck.
To solve this, the Direct Memory Access (DMA) technique is used.
How the DMA Controller Operates:
CPU Delegation: When an I/O transfer is required, the CPU initializes the DMA controller by giving it essential details: whether it is a read or write operation, the peripheral device's address, the starting memory address block in RAM, and the total count of bytes to transfer.
Bus Mastery: Once configured, the DMA controller requests control of the system bus (Data, Address, and Control lines) from the CPU using a Hold Request (HRQ) signal. The CPU finishes its current bus cycle, releases control of the buses, and replies with a Hold Acknowledge (HLDA) signal.
Direct Transfer: With the CPU out of the loop, the DMA controller takes absolute control of the system buses and manages the high-speed data stream directly between the I/O device and main memory, routing it completely around the CPU.
Completion Interrupt: Once the byte counter reaches zero (meaning the whole block is safely moved), the DMA controller relinquishes control of the buses back to the CPU and fires a single hardware Interrupt to let the operating system know that the data is ready for use.
By automating block data transfers in hardware, DMA allows the CPU to execute application logic concurrently, vastly improving system throughput and resource efficiency.