Question

Which one of the following is an important advantage of the DMA mode of data transfer over programmed data transfer?

• A. It reduces memory access time
• B. It improves CPU cycle time
• C. It improves I/O performance by allowing unbuffered transfers
• D. It improves system performance by increasing concurrency

Hint:

DMA improves performance not by making I/O faster alone, but by freeing the CPU to perform other tasks simultaneously.

Answer 1

The Correct Option is D

Step 1: Understanding programmed I/O.
In programmed data transfer, the CPU is actively involved in every data transfer between the I/O device and memory. This keeps the CPU busy and prevents it from performing other useful tasks.
Step 2: Understanding DMA (Direct Memory Access).
In DMA mode, a dedicated DMA controller transfers data directly between the I/O device and the main memory without continuous CPU intervention. The CPU is only involved at the start and end of the transfer.
Step 3: Analyzing the advantage of DMA.
Since the CPU is free while the DMA controller handles data transfer, the CPU can execute other processes concurrently. This leads to better overall utilization of system resources.
Step 4: Final conclusion.
Thus, DMA improves overall system performance by allowing parallel execution of CPU tasks and I/O operations, thereby increasing concurrency.