9. Explain why a serial communications port that manages a terminal keyboard does not normally use the same optimization techniques as a serial communications port that manages a printer.
11. Suppose the read/write head is at track 97, moving toward track 199 (the highest-numbered track on the disk) and the disk request queue contains read/write requests for sectors on tracks 84, 155, 103, 96, and 197, respectively.
a. what is the total number of head movements needed to satisfy the requests in the queue using the FCFS optimization strategy?
b. what is the total number of head movements needed to satisfy the requests in the queue using the Scan optimization strategy?
c. What is the total number of head movements needed to satisfy the requests in the queue using the Look optimization strategy?
(#11: with the read/write head located at 55 and moving toward 0 tack, and the request queue is: 75, 33, 5, 95, 170, and 12).
You must provide detailed steps and explanation to all questions.
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- For FCFS strategy, we have a total number of movements equal to:
55 to 75 to 33 to 5 to 95 to 170 to 12= 20+42+28+90+75+158=413
The values are taken in order, according to FCFS strategy.
- SCAN strategy:
55->0 75, 33, 5, 95, 170, and 12 (increasing order from start until biggest, then through zero and continue in decreasing order of the remaining values)
55 to 75 to 95 to 170 to 0 to 33 to 12 to 5 = 20+20+75+170+33+21+7=346
- LOOK strategy:
- Increasing order until the biggest value and then decreasing
55 to 75 to 95 to 170 to 33 to 12 to 5= 280 movements...