Bsc CSIT Semester 4 – Operating System – Unit 6: Device Management (6 Hrs.)

3. Suppose that the disk drive has 50 cylinders, numbered from 0 to 49.
   The drive is currently serving the request at cylinder 20 and the previous request was at cylinder 25.
   The queue of pending requests is:
   Code

   Copy

   10, 22, 20, 2, 40, 6, 38

   (in this order).
   A seek takes 6 msec per cylinder moved. How much seek time is needed for the following disk-scheduling algorithms?
   • a) First-Come, First-Served (FCFS)
   • b) Shortest Seek Time First (SSTF)
   • c) SCAN
   • d) LOOK

What is “device independence”? Define.

Suppose the head of a moving- head disk with 200 tracks, numbered 0 to 199 is currently serving request at tracks 143 and has finished a request at track 125. The queue it requests is kept in the FIFO order

86, 147, 91, 177, 94, 150, 102, 175, 130

What is DMA? Explain how it works.

How does DMA increase system concurrency? How does it complicate hardware design?

Write short notes on:
(a) Disk formatting
(b) Memory Mapped I/O

What is the main objective of disk scheduling algorithms? why SSTF is not practically feasible? Assume that we have disk with 100 tracks and currently head is at track number 35. What will be the seek time for the algorithms SCAN and LOOK for processing IO requests queue: 52, 67, 27, 11, 43, 85, 18, 75, 92, 8?

When programmed IO is suitable than other IO handling techniques? Explain the process of IO handling using DMA.

Why the concept of disk interleaving is important? Explain with suitable example.

How DMA operation is performed? Consider a disk with 200 tracks and the queue has random requests from different processes in the order :$45, 48, 29, 17, 80, 150, 28$ and $188$. Find the seek time using $FIFO, SSTF$ and $SCAN$. Assume the initial position of head as 100.

Find the seek time using SCAN, C-SCAN, Look and C-Look disk scheduling algorithms for processing

the following request queue:

$35, 70, 45, 15, 65, 20, 80, 90, 75, 130.$

Suppose the disk has tracks numbered from 0 to 150 and assume the disk arm to be at 30 and moving outward.

Explain memory-mapped I/O.

Define shell and system call. suppose a disk has 201 cylinders, numbered from 0 to 200. At same time the disk arm is at cylinder 95, and there is a queue of disk access requests for cylinders 82,170,43,140,24,16 and 190. Calculate the seek time for the disk scheduling algorithm FCFS,SSTF,SCAN and C-SCAN.

Describe the working mechanism of DMA.

What is the task of disk controller ? List some drawback of segmentation.

Suppose a disk has 201 cylinders, numbered from 0 to 200. At same time the disk arm is at cylinder 10, and there is a queue of disk access requests for cylinders $30, 85, 90, 100, 105, 110, 135,$ and $145$. Find the total seek time for the disk scheduling algorithm FCFS and SSTF. Assume the head is moving inward.

What are the advantages of using interrupt? Describe.