Question

Which of the following methods is used for CPU to perform I/O operation?

• A. program initiated I/O
• B. device initiated I/O
• C. direct memory access
• D. serial I/O

Hint:

DMA transfers data directly between memory and device without CPU.

Answer 1

The Correct Option is C

Step 1: See the bottleneck in ordinary I/O.
In programmed and interrupt-driven I/O, every single byte moved between memory and a device has to pass through the CPU, which reads it from one place and writes it to the other. This keeps the CPU busy even though it is not doing any real computation.
Step 2: Hand the job to a dedicated controller instead.
Direct Memory Access solves this by using a separate DMA controller that temporarily takes control of the address and data bus, transferring data straight between the device and memory without routing it through the CPU's registers at all.
Step 3: What the CPU gains from this.
While the DMA controller handles the bulk transfer, the CPU is free to execute other instructions, and it only gets involved briefly at the start to set up the transfer and again at the end when it finishes. This makes DMA the preferred method for fast, high-volume transfers like disk or memory-to-memory operations.
\[ \boxed{\text{direct memory access}} \]