Which one of the following facilitates transfer of bulk data from hard disk to main memory with the highest throughput?
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Answer: A
To transfer bulk data from a high-speed storage device like a hard disk to the main memory efficiently, we need to minimize CPU intervention during the transfer process.
- Programmed I/O and Polling (Options C and D): The CPU must constantly monitor the device status and manage the transfer of every single word. This wastes significant CPU cycles and results in very low throughput.
- Interrupt-driven I/O (Option B): While it frees the CPU from actively waiting, the CPU is still interrupted for every word/byte transferred. The overhead of context switching for each small unit of data makes it unsuitable for high-speed bulk data transfers.
- DMA (Direct Memory Access) based I/O transfer (Option A): The DMA controller takes control of the system bus to transfer entire blocks of data directly between the hard disk and main memory. The CPU is only involved at the start (to initialize the transfer parameters) and at the end (to receive a completion interrupt). This bypasses the CPU bottleneck, providing the highest throughput for bulk data.
Therefore, DMA based I/O transfer is the most efficient method for bulk data transfer.
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