Question $1$

A disk queue is holding requests to the following cylinders in the order: $110,12,15,20,70,145,90,80.$ What is the order that the requests are serviced for the

algorithms listed below, assuming the disk head is at cylinder $45.$ The disk has a total of $200$ cylinders $(0-199).$ Hint: For SCAN, pay attention to the direction

the read$/$write head is moving. $(4$ marks$)$

A$.$ FCFS scheduling

B$.$ SCAN scheduling $($arm is moving from cylinder $45$ towards cylinder $0)$

C$.$ C$-$SCAN scheduling

D$.$ Which algorithm gives the best result $($i$.$e$.,$ services all the requests with the minimum amount of head movement$).$

Question $2$

A disk queue is holding requests to the following cylinders in the order: $115,13,25,35,75,155,100,90.$ What is the order that the requests are serviced, for

the algorithms listed below, assuming the disk head is at cylinder $85..$ The disk has a total of $200$ cylinders $(0-199).$ Hint: For SCAN, be sure to pay attention to

the direction the read$/$write head is moving. $(4$ marks$)$

A$.$ FCFS scheduling

B$.$ SCAN scheduling $($arm is moving right from cylinder $85$ towards cylinder $0)$

C$.$ C$-$SCAN scheduling

D$.$ Which algorithm gives the worst result $($i$.$e$.,$ services all the requests but requires the maximum amount of head movement$).$

Question $3$

Consider a legacy disk drive with a sector size of $512$ bytes, $128$ tracks per surface and $500$ sectors per track. The disk has $5$ double$-$sided platters. $(3$ marks$)$

A$.$ Calculate capacity of a track in bytes? What is the capacity of each surface? What is the capacity of the disk?

B$.$ How many cylinders does the disk have?

C$.$ Give three examples of valid block sizes.

Question $4$

Assume that a hard disk rotates at $15,000$ revolutions per minute $($rpm$).$ Each track of the disk has $500$ sectors$.$ The average seek time of disk is $8$

milliseconds. Calculate the average access time for this disk. Hint: the average rotation time is $\frac{1}{2}$ of the maximum rotation time. $(4$ marks$)$

Disk Rotation Speed $=15,000rpm$

Sectors per Track $=500$ sectors

Average seek time $=8$ millisecond