Question

(1.5) Rank (highest first/left-most to lowest last/right-most) the following three techniques based on number of interrupts generated: (a) programmed I/O, (b) interrupt-driven I/O, and (c) Direct Memory Access (DMA).

(1.6) Rank (highest first, lowest last) the following three techniques based on wait time/wasted CPU cycles (including interrupt handling): (a) programmed I/O, (b) interrupt-driven I/O, and (c) Direct Memory Access (DMA).

(1.7) On the same OS, on the same uniprocessor machine, two different processes 20 and 30 open the same file named abcd.txt . Will the file descriptors associated with abcd.txt be always the same ? Give a YES or NO answer.

Answer 1

1.5. Interrupt Driven I/O, Direct Memory Access, Programmed I/O

Reason: In programmed I/O, CPU continuously checks whether I/O is ready for data transfer. This method is not dependent on Interrupts. In interrupt driven I/O, CPU can engage in other work. Whenever I/O is ready, an Interrupt signal is generated to notify CPU. This method is heavily dependent on Interrupts - Every word/block transfer leads to interrupt signal. In DMA, CPU is not directly involved. Data transfer directly occurs between memory and I/O and CPU is notified by Interrupt when the transfer completes.

1.6. programmed I/O, interrupt-driven I/O, Direct Memory Access

Reason: As mentioned above, in programmed I/O, CPU is continuously engaged in a busy wait checking whether I/O is ready. So wait time/wasted cycle is highest here. In Interrupt driven I/O, CPU is free to engage in other work but whenever an interrupt signal cones, it has to stop the work and engage in data transfer. In DMA, the CPU is not directly involved in the transfer and hence is idle while direct transfer occur between memory and I/O.

1.7. No, reason being each process has its own file descriptor table. File descriptor for a file in process a can be different from file descriptor of process b even if they access the same file.