Operating Systems Exam 3 Questions with Correct Answers Latest Update 2025/2026
What are the two components of positioning time? - Answers seek time + rotational latency
Which of the following statements regarding solid state disks (SSDs) is false?
1. They have no seek time or latency.
2. They are generally more expensive per megabyte than traditional hard disks.
3. They have the same characteristics as magnetic hard disks, but can be more reliable.
4. They generally consume more power than traditional hard disks. - Answers They generally
consume more power than traditional hard disks
An advantage of SSDs over HDDs is
1. SSDs are cheaper per megabyte than HDDs.
2. SSDs are more reliable than HDDs.
3. SSDs are faster than HDDs. - Answers 2. and 3.
Number of sectors per track increases as we move from inner zone to outer zone, because -
Answers the outer zones have a larger circumference, allowing more sectors to fit on each track
Which of the following disk head scheduling algorithms does not take into account the current
position of the disk head?
1. C-SCAN
2. SCAN
3. FCFS
4. All scheduling algorithms take into account the current position of the disk head - Answers
FCFS
The SCAN scheduling algorithm ____. - Answers services the request next to the current head
position in the direction of the head movement
Consider a disk queue holding requests to the following cylinders in the listed order: 116, 22, 3,
11, 75, 185, 100, 87. Using the SCAN scheduling algorithm, what is the order that the requests
are serviced, assuming the disk head is at cylinder 88 and moving upward through the cylinders?
- Answers 100-116-185-87-75-22-11-3
Consider a disk queue holding requests to the following cylinders in the listed order: 210, 67, 11,
99, 87, 90, 19, 150. Using the C-SCAN scheduling algorithm, what is the order that the requests
, are serviced, assuming the disk head is at cylinder 88 and moving upward through the cylinders?
- Answers 90-99-150-210-11-19-67-87
A track is the smallest unit of data transfer in a hard disk drive. - Answers False (logical block)
SCAN disk head scheduling offers no practical benefit over FCFS disk head scheduling. -
Answers False
In general, SCAN disk head scheduling will involve less movement of the disk heads than C-
SCAN disk head scheduling. - Answers True
SSTF Scheduling Algorithm - Answers Selects the request with the minimum seek time from the
current head position.
SCAN Scheduling Algorithm - Answers Disk arm starts at one end of the disk, and moves toward
the other end of the disk, where the head movement is reversed and servicing continues
C-SCAN Scheduling Algorithm - Answers The head moves from one end of the disk to the other,
servicing requests as it goes.
When it reaches the other end, it immediately returns to the beginning of the disk, without
servicing any requests on the return trip.
Prevents starvation.
C-LOOK Scheduling Algorithm - Answers Version of C-SCAN
Arm only goes as far as the last request in each direction, then reverses direction immediately,
without first going all the way to the end of the disk.
Mapping - Answers Sector 0: first sector of first track on outermost cylinder.
Mapping proceeds through track, then rest of tracks in cylinder, then rest of cylinders from outer
to innermost.
A current trend in I/O device technology and I/O subsystem is - Answers there is an increasingly
broad variety of I/O devices.
In polling I/O, the main inefficiency comes from - Answers polling when it is attempted
repeatedly yet rarely finds a device ready for service.
interrupt chaining - Answers is a compromise between the overhead of a huge interrupt table
and the inefficiency of dispatching to a single interrupt hander.
In DMA-based I/O, - Answers cycle stealing can slow down the CPU computation, but off-loading
the data-transfer work to a DMA controller generally improves the total system performance.
In a blocking system call, the execution of a process is suspended - Answers until the I/O has
What are the two components of positioning time? - Answers seek time + rotational latency
Which of the following statements regarding solid state disks (SSDs) is false?
1. They have no seek time or latency.
2. They are generally more expensive per megabyte than traditional hard disks.
3. They have the same characteristics as magnetic hard disks, but can be more reliable.
4. They generally consume more power than traditional hard disks. - Answers They generally
consume more power than traditional hard disks
An advantage of SSDs over HDDs is
1. SSDs are cheaper per megabyte than HDDs.
2. SSDs are more reliable than HDDs.
3. SSDs are faster than HDDs. - Answers 2. and 3.
Number of sectors per track increases as we move from inner zone to outer zone, because -
Answers the outer zones have a larger circumference, allowing more sectors to fit on each track
Which of the following disk head scheduling algorithms does not take into account the current
position of the disk head?
1. C-SCAN
2. SCAN
3. FCFS
4. All scheduling algorithms take into account the current position of the disk head - Answers
FCFS
The SCAN scheduling algorithm ____. - Answers services the request next to the current head
position in the direction of the head movement
Consider a disk queue holding requests to the following cylinders in the listed order: 116, 22, 3,
11, 75, 185, 100, 87. Using the SCAN scheduling algorithm, what is the order that the requests
are serviced, assuming the disk head is at cylinder 88 and moving upward through the cylinders?
- Answers 100-116-185-87-75-22-11-3
Consider a disk queue holding requests to the following cylinders in the listed order: 210, 67, 11,
99, 87, 90, 19, 150. Using the C-SCAN scheduling algorithm, what is the order that the requests
, are serviced, assuming the disk head is at cylinder 88 and moving upward through the cylinders?
- Answers 90-99-150-210-11-19-67-87
A track is the smallest unit of data transfer in a hard disk drive. - Answers False (logical block)
SCAN disk head scheduling offers no practical benefit over FCFS disk head scheduling. -
Answers False
In general, SCAN disk head scheduling will involve less movement of the disk heads than C-
SCAN disk head scheduling. - Answers True
SSTF Scheduling Algorithm - Answers Selects the request with the minimum seek time from the
current head position.
SCAN Scheduling Algorithm - Answers Disk arm starts at one end of the disk, and moves toward
the other end of the disk, where the head movement is reversed and servicing continues
C-SCAN Scheduling Algorithm - Answers The head moves from one end of the disk to the other,
servicing requests as it goes.
When it reaches the other end, it immediately returns to the beginning of the disk, without
servicing any requests on the return trip.
Prevents starvation.
C-LOOK Scheduling Algorithm - Answers Version of C-SCAN
Arm only goes as far as the last request in each direction, then reverses direction immediately,
without first going all the way to the end of the disk.
Mapping - Answers Sector 0: first sector of first track on outermost cylinder.
Mapping proceeds through track, then rest of tracks in cylinder, then rest of cylinders from outer
to innermost.
A current trend in I/O device technology and I/O subsystem is - Answers there is an increasingly
broad variety of I/O devices.
In polling I/O, the main inefficiency comes from - Answers polling when it is attempted
repeatedly yet rarely finds a device ready for service.
interrupt chaining - Answers is a compromise between the overhead of a huge interrupt table
and the inefficiency of dispatching to a single interrupt hander.
In DMA-based I/O, - Answers cycle stealing can slow down the CPU computation, but off-loading
the data-transfer work to a DMA controller generally improves the total system performance.
In a blocking system call, the execution of a process is suspended - Answers until the I/O has
