Question

Which one of the following statements is FALSE?

• A. In the cycle stealing mode of DMA, one word of data is transferred between an I/O device and main memory in a stolen cycle.
• B. For bulk data transfer, the burst mode of DMA has a higher throughput than the cycle stealing mode.
• C. Programmed I/O mechanism has a better CPU utilization than the interrupt-driven I/O mechanism.
• D. The CPU can start executing an interrupt service routine faster with vectored interrupts than with non-vectored interrupts.

Hint:

Programmed I/O involves continuous polling by the CPU, leading to inefficient use of resources. Interrupt-driven I/O allows better CPU utilization by enabling multitasking.

Answer 1

The Correct Option is C

Step 1: Analyze the statements.
1. Cycle stealing mode in DMA: In this mode, the DMA controller temporarily "steals" cycles from the CPU to transfer one word of data. This is a valid statement.
2. Burst mode in DMA: Burst mode transfers large blocks of data at once, resulting in higher throughput compared to cycle stealing mode. This is also a valid statement.
3. Programmed I/O vs. Interrupt-driven I/O: Programmed I/O requires the CPU to continuously poll the device, leading to inefficient CPU utilization. Interrupt-driven I/O, on the other hand, allows the CPU to perform other tasks until the device signals it. Hence, this statement is FALSE.
4. Vectored interrupts: Vectored interrupts have predefined addresses for the interrupt service routines, allowing faster execution compared to non-vectored interrupts, which require additional steps to determine the address. This statement is TRUE. Final Answer: \[ \boxed{\text{Programmed I/O mechanism has a better CPU utilization than the interrupt-driven I/O mechanism.}} \]