1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
maria [59]
3 years ago
6

Disk requests come in to the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that order. A seek takes 6 msec per cyli

nder moved. The arm is initially at cylinder 20.
How much seek time is needed if


a) FCFS


b) SSTF


c) SCAN (elevator)


algorithm is employed?
Computers and Technology
1 answer:
oksano4ka [1.4K]3 years ago
6 0

Answer:

For  FCFS = 876msec For SSTF = 360msec For SCAN(elevator) = 348msec

Explanation:

Considering FCFS algorithm.

In FCFS, the requests are addressed in the order they arrive in the disk queue, this means that the number of cylinders traveled becomes equal to the total of disk requests. With the arm initially at 20, the first request is to read cylinder 10.

Therefore the cylinders traversed for the first request = 20 – 10 = 10  

For the second request i.e. a movement from cylinder 10 to cylinder 22, the number of cylinders traversed is = 22 - 10 = 12.

Similarly, for the third request seek arm will return to 20 from 22 so, cylinders traversed through would be = 22-20 = 2.    

Also for the fourth request, cylinders traversed would be = 20 – 2 = 18.

For the fifth request, cylinders traversed = 40 – 2 = 38.

Now for the sixth request cylinders traversed = 40 – 6 = 34.

For the seventh and last request, cylinders traversed = 38 – 6 = 32.

So now to get the how much seek time is required for Disk scheduling algorithm  

First we would add the total cylinders traversed = 10 + 12 + 2+ 18+ 38 + 34 + 32

     = 146 cylinders  

So therefore the total seek time = number of cylinders traversed X seek time per cylinder

               = 146 X 6

   = 876msec

Considering SSTF algorithm.

In SSTF (Shortest Seek Time First), requests having shortest seek time are executed first. So, the seek time of every request is calculated in advance in the queue and then they are scheduled according to their calculated seek time. What this means is that the closest disk (cylinder) next to the position of the seek arm is attended to first. With   the arm at 20 initially, the first request is to read cylinder 22 (i.e. the closest cylinder to the seek arm)

Therefore the cylinders traversed for the first request = 22-20 = 2

For the second request, the disk to focus on is disk 20 and the cylinders traversed = 22-20 = 2

Similarly for the third request the seek arm will move to 10 from 20 so, cylinder traversed = 20-10 =10

For fourth request, cylinder traversed = 10 – 6 = 4

For the fifth request, cylinder traversed = 6 – 2 = 4

For sixth request, since all other disk request closer to it has been attended to the seek arm will move to disk 38 to attend to that disk request So, the cylinder traversed = 38 – 2 = 36

For the last request, cylinder traversed = 40 -38 = 2

So now to get the how much seek time is required for Disk scheduling algorithm  

First we would add the total cylinders traversed = 2 + 2 +10 + 4 + 4 + 36 + 2  

     = 60 cylinders

So therefore the total seek time = number of cylinders traversed X seek time per cylinder

     = 60 X 6 = 360msec

From Here we see that SSTF is better or an improvement to FCFS as it decrease the average response time (Average Response time is the response time of the all requests).

Considering SCAN (elevator) algorithm  

In SCAN algorithm the disk arm moves into a particular direction and services the requests coming in its path and after reaching the end of disk, it reverses its direction and again services the request arriving in its path. So, this algorithm works as an elevator and hence also known as elevator algorithm. Therefore the number of cylinder traveled becomes equal to the total of disk request. With the arm at 20 initially

The first request is to read cylinder 22 i.e. the first cylinder on the upward movement  

Therefore the cylinders traversed would be  =   20 – 22 = 2

For the second request is to read cylinder 38, and the cylinders traversed would be   = 38 – 22 =16

For the third request, seek arm will move to 40 So, the cylinders traversed would be = 40 – 38 = 2

For the fourth request, seek arm will return to 20 since from 40 since 40 is the highest in this upward elevator movement So, cylinders traversed would be = 40 -20 = 20  

For the fifth request, cylinder traversed would be = 20 – 10 = 10

For the sixth request, cylinder traversed would be   = 10 – 6 = 4

For the seventh and last request, cylinder traversed = 6 – 2 = 4

So now to get the how much seek time is required for Disk scheduling algorithm  

First we would add the total cylinders traversed = 2 + 16 + 2 + 20 +10+ 4 + 4 = 58 cylinders

So therefore the total seek time = number of cylinders traversed X seek time per cylinder

   = 58 X 6

          = 348msec

From Here we see that SCAN is better or an improvement to FCFS and SSTF as it decrease the average response time (Average Response time is the response time of the all requests).

You might be interested in
In the LC-3, how many memory words are used to store the string "rainbow"?
oksian1 [2.3K]
The number of memory words used to store the string "rainbow" is 8.
5 0
3 years ago
In discussing inventory, Helena mentions that bikinis for sale on the website are not always in stock. Say customer feedback ind
alekssr [168]

Answer:

decide that when online customers and retail stores order bikinis, they will never have to wait more than two weeks for the order to arrive.

Explanation:

Based on the information provided within the question it can be said that in this scenario the best action that Helena can take is to decide that when online customers and retail stores order bikinis, they will never have to wait more than two weeks for the order to arrive. Otherwise she will begin to lose customers constantly by not having stock or shipping the product in time. These losses will continue to amass and may eventually ruin her business.

6 0
3 years ago
Which strategy should individuals working in a diverse workplace adopt?
yawa3891 [41]
B.Interact more with people from different backgrounds. this is correct because that would help people get to know each other better.

Hope this helps:)
4 0
3 years ago
Read 2 more answers
I need help with this question. asap please
marissa [1.9K]

Answer:

what are you talking about

Explanation:

can you help me with my question

8 0
2 years ago
A short
alexandr402 [8]

Explanation:

Java Bitwise Operators

Operator Description Example

>> (right shift) Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand. A >> 2 will give 15 which is

8 0
3 years ago
Other questions:
  • Which area of the network would a college it staff most likely have to redesign as a direct result of many students bringing the
    10·1 answer
  • Suppose you are currently in the /home/hnewman/os/fall/2013 directory and would like to navigate to /home/hnewman/discreteStruct
    9·1 answer
  • O novo funcionário da equipe de desenvolvimento de sistemas está aprendendo os termos mais utilizados no dia a dia da empresa. A
    7·1 answer
  • Name the two types of control systems.<br> PLEASE HELP THIS WAS DUE HOURS AGOOOO
    8·2 answers
  • A storyboard is an example of an implementation tool.
    8·1 answer
  • What is the major benefit Smartphones and tablet computers have had on social media?
    9·1 answer
  • Mika forgot to put in the function name in his function header for the code below. What would be the best function header?
    12·2 answers
  • Write a python application that allows a user to enter any number of student test scores until the user enters 999. If the score
    14·1 answer
  • Write a Temperature class that represents temperatures in degrees in both Celsius and Fahrenheit. Use a floating-point number fo
    5·1 answer
  • your manager asked you to set up a secure network connection at a remote site to move over some back ups. what protocol what do
    8·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!