OS_DISK_SCHEDULING

Suppose that a disk drive has 2000 cylinders, numbered 0 to 1999. The drive is currently serving a request at cylinder 143, and the previous request was at cylinder 125. The queue of pending requests, in FIFO order, is 86, 1470, 913, 1774, 948, 1509, 1022, 1750, and 130. Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for the SSTF disk-scheduling algorithm?

• 2000

• 1745

• 1650

• 1800

• 1550

The seek time is defined as the time

• required by the read/write head to move from one track to another

• required by the read/write head to rotate to the requested sector from the current sector

• to transfer the data from the hard disk to the main memory

• to rotate the read/write head to place it in the desired sector

Which of the following is known as the elevator algorithm?

• FCFS

• SSTF

• SCAN

• LOOK

Suppose that a disk drive has 120 cylinders numbered 0 to 119. Consider a disk request with I/O requests on the following cylinders in their arriving order: 67, 12, 15, 45, 48, 50, 109, 89, 56, 59, 34, 88, 113, 24, and 22. The disk head is assumed to be at cylinder 80. Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for the FCFS disk-scheduling algorithm?

• 350

• 442

• 550

• 660

Suppose that a disk drive has 200 cylinders numbered 0 to 199. Consider a disk queue with requests for I/O to blocks on cylinders 100, 187, 47, 112, 18, 144, 55, and 70, in that order. Assume that the head is moving toward increasing the order of the cylinder numbers. Initially, the disk head is at cylinder 50. Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for the C-SCAN disk-scheduling algorithm?

• 50

• 395

• 100

• 75

Which of the following disk scheduling algorithm eliminates unnecessary seek operations and increase the average response time?

• SCAN

• LOOK

• SSTF

• FCFS

Suppose that a disk drive has 150 cylinders numbered 0 to 149. Consider a disk queue with I/O requests on the following cylinders in their arriving order: 6, 10, 12, 54, 97, 73, 128, 15, 44, 110, 34, and 45. The read/write head is positioned at cylinder 23 and moving in the direction of decreasing cylinder number. Starting from the current head position 23, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for the LOOK disk-scheduling algorithm?

• 119

• 139

• 150

• 100

Suppose that a disk drive has 150 cylinders numbered 0 to 149. Consider a disk queue with I/O requests on the following cylinders in their arriving order: 6, 10, 12, 54, 97, 73, 128, 15, 44, 110, 34, and 45. The read/write head is positioned at cylinder 23 and moving in the direction of decreasing cylinder number. Starting from the current head position 23, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for the C-LOOK disk-scheduling algorithm?

• 233

• 133

• 140

• 220

RAID structure is used to

• improve the performance of the data storage system

• make the data storage system fault-tolerant

• improve the data recover

• improve the reliability of the data storage system

• All of the above

The bit map technique is used in file systems to

• manage the file permissions

• keep track of available and allocated disk blocks or sectors

• index the file names

• store the file data