Unit 8 : Disk Management

Question 1

What is the lowest level of a file system?

Answer 1

1. Secondary Storage ( Hard Drive )

Question 2

What is the first secondary storage?

Answer 2

1. Magnetic Tape

• Magnetic Tapes access time is slow compared to disk

Question 3

What is tape is now used for?

Answer 3

1. Storage and Backup of infrequently used data

Question 4

What part of computer is responsible to use hardware efficiently?

Answer 4

1. Operating System

Question 5

What is the standard ( criteria ) for disk drivers? ( 2 )

Answer 5

1. Fast Access Time
2. Increase Disk Bandwidth

Question 6

List out 2 parts of access time in Hard Drive

Answer 6

1. Seek Time
   
   • Time for the disk arm to move to the head of the cylinder containing the desired sector
2. Rotational Latency
   
   • Additional time waiting for the disk to rotate to the desired sector of the disk head

Question 7

What is a track on a hard drive?

Answer 7

1. Concentric circles on a platter where data is stored

• More on notion

Question 8

What component is a thin, circular disk within a hard drive that stores data?

Answer 8

1. Platter

Question 9

What is the smallest physical unit of data storage within a track?

Answer 9

1. Track Sector

• 512 bytes or 4096 bytes in size

Question 10

Which component groups sectors to help reduce file fragmentation?

Answer 10

1. Cluster

Question 11

What part of the hard drive contains a magnetic read/write head?

Answer 11

1. Head

Question 12

What is the purpose of the actuator arm in a hard drive?

Answer 12

1. To position the head over the correct track to read or write data

Question 13

How can we improve access time and bandwidth of Hard Drive?

Answer 13

1. Scheduling the services of disk, I/O requests in a good order

Question 14

What are the steps when a process needs I/O to or from the disk? ( 3 )

Answer 14

1. Systems calls are issued to the operating system
2. IF disk is AVAILABLE, the request is serviced
3. IF disk is NOT AVAILABLE, the request is placed on queue

Question 15

List out the disk scheduling algorithms ( 6 )

Answer 15

1. First Come First Serve ( FCFS )
2. Shortest Seek Time First ( SSTF )
3. Scan
4. C-Scan
5. Look
6. C-Look

Question 16

What is the simplest disk scheduling algorithms?

Answer 16

1. First Come First Serve ( FCFS )

• It is fair but it does not provide the fastest service
• As its name, the first process will be processing first

Question 17

What disk scheduling algorithms minimized seek time?

Answer 17

1. Shortest Seek Time First

• It will first service that are closest to the current head position
• Requests can arrive at any time, request furthest from the head will need to wait before getting serviced

Question 18

What disk scheduling algorithms is known as having the elevator syndrome?

Answer 18

1. Scan

• Like elevator go up / down first, then only goes down / up
• Disk starts at one end and moves towards the other end
• Head will reverses and moves back and it will serves the requests when it was moving back

Question 19

What page replacement algorithms has the following :
1. Like Scan
2. It is a circular scan

Answer 19

1. C-Scan

• It starts from the head and moves to an end ( 199 ), then the arm moves back without servicing any request

Question 20

What is the difference between Look and Scan?

Answer 20

1. Look goes for the final request, while Scan moves the head from the beginning to the end

• Look does not went to the end of the disk

Question 21

What does C-Look do?

Answer 21

1. Starts from the current head and moves towards the end
2. Stops at the last request without going to the end of the disk
3. Reverses without serving any request

Question 22

What is the aim for Disk Scheduling Algorithms? ( 2 )

Answer 22

1. Reduce seek time
2. Reduce rotational latency while increasing bandwidth