Disk Scheduling Algorithms MCQ 60 Practice Tests With Answers (2026)
PerfectNotes TeamUpdated: March 2026~15 min practice 60 Questions · 3 Levels 60 Questions · 3 Levels
A core function of an Operating System is abstracting complex, physical magnetic disks into logical, easily accessible storage structures. These 60 carefully structured Disk Scheduling Algorithms MCQs evaluate your architectural knowledge of how I/O requests are ordered, optimized, and dispatched to maximize disk throughput.
These questions are organized into three progressive difficulty levels of 20 questions each: Basics (covering FCFS, SSTF, SCAN fundamentals, seek time, cylinder geometry, and starvation), Concepts (covering C-SCAN, LOOK, C-LOOK, N-Step-SCAN, RPO, FSCAN, and Deadline scheduler), and Advanced (covering NCQ, SATF, CFQ, BFQ, kyber, NVMe parallel queuing, anticipatory scheduling, ZBR, and SAN queue depth). Each question features comprehensive explanations connecting theory to practice.
Use Study Mode to build an architectural mental model by revealing concepts interactively, or use Exam Mode to simulate technical assessments and university exam conditions with timed tracking and instant scoring.
Contents
- 1.Basics (20 Questions)FCFS · SSTF · SCAN · Seek time · Starvation
- 2.Concepts (20 Questions)C-SCAN · LOOK · C-LOOK · Deadline · N-Step-SCAN
- 3.Advanced (20 Questions)NCQ · CFQ · BFQ · NVMe queues · ZBR · SAN
- 4.Conclusionsummary · next steps · study tips
- 5.Key Takeawaysquick-fire bullet recap of essential facts
- 6.Quick Review Summaryconcept · definition · key fact table
- 7.FAQcommon questions answered
Disk Scheduling Algorithms — Basics
1What is the primary objective of disk scheduling algorithms in an operating system?
CorrectA: To minimize the mechanical seek time required to move the read/write head across the disk cylinders
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: To minimize the mechanical seek time required to move the read/write head across the disk cylinders
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
2Which disk scheduling algorithm services I/O requests strictly in the chronological order they arrive in the queue?
CorrectB: FCFS
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: FCFS
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
3In the context of disk scheduling, what does the acronym "SSTF" stand for?
CorrectC: Shortest Seek Time First
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: Shortest Seek Time First
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
4Which disk scheduling algorithm is widely referred to as the "Elevator" algorithm?
CorrectD: SCAN
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: SCAN
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
5In the standard SCAN algorithm, what specific behavior occurs when the read/write head reaches the physical end of the disk?
CorrectA: It immediately reverses its direction of travel and services requests on the way back
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: It immediately reverses its direction of travel and services requests on the way back
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
6What is the defining characteristic of the C-SCAN algorithm compared to the standard SCAN algorithm?
CorrectB: It strictly services requests in one single direction, providing a more uniform wait time
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: It strictly services requests in one single direction, providing a more uniform wait time
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
7What does the "C" in the algorithms C-SCAN and C-LOOK stand for?
CorrectC: Circular
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: Circular
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
8Which algorithm optimizes the SCAN method by reversing direction immediately after servicing the final request in a given direction, rather than traveling pointlessly to the absolute physical edge of the disk?
CorrectD: LOOK
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: LOOK
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
9In disk terminology, what specifically constitutes "Seek Time"?
CorrectB: The time required for the mechanical actuator arm to laterally move the read/write head to the correct cylinder
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: The time required for the mechanical actuator arm to laterally move the read/write head to the correct cylinder
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
10Why is the FCFS algorithm generally considered sub-optimal for heavy, concurrent disk workloads?
CorrectC: It ignores the physical layout of the requests, causing erratic, highly inefficient "wild swings" of the read/write head
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: It ignores the physical layout of the requests, causing erratic, highly inefficient "wild swings" of the read/write head
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
11In the C-LOOK algorithm, what happens when the read/write head finishes the absolute highest cylinder request in its current sweeping direction?
CorrectD: It rapidly jumps back to the lowest requested cylinder in the queue without servicing any requests on the return trip
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: It rapidly jumps back to the lowest requested cylinder in the queue without servicing any requests on the return trip
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
12Which physical factor does traditional disk scheduling (like SSTF and SCAN) primarily attempt to minimize?
CorrectA: Mechanical seek distance across the disk platters
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: Mechanical seek distance across the disk platters
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
13If a disk queue currently contains requests for cylinders 10, 50, and 90, and the read/write head is currently resting at cylinder 45, which request will the SSTF algorithm process first?
CorrectB: 50
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: 50
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
14What type of data structure is natively used to implement the pure FCFS disk scheduling algorithm?
CorrectC: A standard FIFO (First-In, First-Out) Queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: A standard FIFO (First-In, First-Out) Queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
15Which of the following enterprise storage mediums benefits the *least* from traditional, geometry-based disk scheduling algorithms?
CorrectD: Non-Volatile Memory Express (NVMe) Solid State Drives
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: Non-Volatile Memory Express (NVMe) Solid State Drives
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
16In the context of disk scheduling workloads, what is "Starvation"?
CorrectA: A scenario where a specific I/O request is continually bypassed and never serviced due to a constant influx of higher-priority or closer requests
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: A scenario where a specific I/O request is continually bypassed and never serviced due to a constant influx of higher-priority or closer requests
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
17Which of the following fundamental scheduling algorithms is most notorious for potentially causing severe request starvation?
CorrectC: SSTF
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: SSTF
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
18How does the standard C-SCAN algorithm handle the mechanical return trip after reaching the absolute end of the disk?
CorrectD: It swings the head rapidly back to cylinder zero without reading or writing any data payloads
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: It swings the head rapidly back to cylinder zero without reading or writing any data payloads
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
19What specific hardware component actually executes the mechanical movements dictated by the operating system's disk scheduling algorithm?
CorrectA: The Actuator Arm
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: The Actuator Arm
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
20If the disk scheduling request queue is entirely empty, what action does the algorithm take?
CorrectB: It simply leaves the read/write head resting at its current position or parked, awaiting the next I/O request
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: It simply leaves the read/write head resting at its current position or parked, awaiting the next I/O request
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
Disk Scheduling Algorithms — Concepts
1Why does the C-SCAN algorithm inherently provide a more uniform wait time across the entire disk than the standard SCAN algorithm?
CorrectC: Because the center tracks aren't serviced twice as often as the extreme edge tracks during a full mechanical round trip
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: Because the center tracks aren't serviced twice as often as the extreme edge tracks during a full mechanical round trip
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
2A disk features cylinders numbered 0 to 199. The head is currently at cylinder 100 and moving towards 199. The active queue is [120, 190, 10, 20]. Under the standard SCAN algorithm, which request is serviced *first*?
CorrectD: 120
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: 120
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
3Using the same scenario (Cylinders 0-199, Head at 100 moving up, Queue: [120, 190, 10, 20]), which request is serviced *last* under the C-LOOK algorithm?
CorrectA: 20
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: 20
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
4What is the precise operational difference between the SCAN and LOOK algorithms?
CorrectB: SCAN forces the head to travel to the absolute physical cylinder limit (0 or MAX), whereas LOOK intelligently reverses direction at the lowest or highest requested cylinder
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: SCAN forces the head to travel to the absolute physical cylinder limit (0 or MAX), whereas LOOK intelligently reverses direction at the lowest or highest requested cylinder
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
5Why is SSTF generally preferred over FCFS in most practical, moderate-load computing environments?
CorrectC: It drastically reduces the total aggregate head movement by always picking the closest target, maximizing overall throughput
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: It drastically reduces the total aggregate head movement by always picking the closest target, maximizing overall throughput
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
6What specific workload pattern heavily exacerbates the starvation anomaly inherent in the SSTF algorithm?
CorrectD: A continuous, heavy stream of new I/O requests arriving clustered tightly around the current head position
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: A continuous, heavy stream of new I/O requests arriving clustered tightly around the current head position
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
7Which scheduling algorithm conceptually mimics the mechanical movement of a windshield wiper clearing rain off a curved glass surface?
CorrectA: SCAN
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: SCAN
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
8The request queue is [98, 183, 37] and the head is currently at 53. Under the FCFS algorithm, what is the total absolute head movement (in cylinders) required to service the first *two* requests in the queue?
CorrectB: 130
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: 130
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
9How does the operating system typically resolve a tie in the SSTF algorithm if two queued requests are exactly equidistant from the current head position?
CorrectD: It defaults to the request that arrived in the queue first, or aligns with the current rotational trajectory of the platter
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: It defaults to the request that arrived in the queue first, or aligns with the current rotational trajectory of the platter
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
10Which of the following represents a significant software processing drawback of the C-LOOK algorithm compared to C-SCAN?
CorrectA: C-LOOK requires the OS to constantly calculate and locate the absolute lowest and highest cylinder requests in the active queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: C-LOOK requires the OS to constantly calculate and locate the absolute lowest and highest cylinder requests in the active queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
11Under incredibly heavy, sustained I/O loads, why does SCAN generally provide better overall system throughput than SSTF?
CorrectB: It prevents the head from oscillating rapidly in a localized area, enforcing a highly structured, organized traversal of the entire disk
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: It prevents the head from oscillating rapidly in a localized area, enforcing a highly structured, organized traversal of the entire disk
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
12In a modified "N-Step-SCAN" algorithm, how does the system proactively prevent newly arriving requests from causing starvation?
CorrectC: It divides the queue into sub-queues of length N, and completely services one sub-queue before adding any new requests to the active batch
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: It divides the queue into sub-queues of length N, and completely services one sub-queue before adding any new requests to the active batch
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
13What is the fundamental concept behind "Rotational Positional Optimization" (RPO) in advanced disk scheduling?
CorrectD: Factoring in the spinning angular position of the platter, not just the lateral cylinder distance, to decide the absolute fastest next request
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: Factoring in the spinning angular position of the platter, not just the lateral cylinder distance, to decide the absolute fastest next request
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
14The read/write head is at cylinder 50. The active queue contains requests [46, 60, 30, 70]. What exact sequence of cylinders does the pure SSTF algorithm follow?
CorrectA: 50 -> 46 -> 60 -> 70 -> 30
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: 50 -> 46 -> 60 -> 70 -> 30
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
15What is the primary architectural difference between FSCAN and standard SCAN?
CorrectB: FSCAN uses two separate queues; while sweeping to service one queue, all new incoming requests are deferred to the second, frozen queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: FSCAN uses two separate queues; while sweeping to service one queue, all new incoming requests are deferred to the second, frozen queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
16Why might an operating system intentionally delay servicing a disk request even if the read/write head is currently positioned on the correct cylinder?
CorrectC: To allow a batch of contiguous write requests to accumulate in RAM, enabling a single, massive sequential write operation
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: To allow a batch of contiguous write requests to accumulate in RAM, enabling a single, massive sequential write operation
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
17In modern enterprise operating systems, where does the final, definitive sorting of the disk scheduling queue typically take place?
CorrectB: Directly on the disk controller's internal hardware firmware, rather than entirely within the OS kernel
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: Directly on the disk controller's internal hardware firmware, rather than entirely within the OS kernel
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
18What is the mathematical maximum possible head movement (in cylinders) for a single request in the FCFS algorithm on a disk containing *N* total cylinders?
CorrectC: N - 1
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: N - 1
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
19Which of the following scheduling algorithms is fundamentally a "Greedy" algorithm, meaning it aggressively picks the best local choice but is highly sub-optimal globally?
CorrectD: SSTF
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: SSTF
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
20How does the "Deadline" scheduling algorithm (utilized heavily in Linux environments) effectively balance raw performance with fairness?
CorrectA: It maintains a standard sorted I/O queue alongside a secondary queue strictly ordered by expiration timers, forcing service before severe starvation occurs
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: It maintains a standard sorted I/O queue alongside a secondary queue strictly ordered by expiration timers, forcing service before severe starvation occurs
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
Disk Scheduling Algorithms — Advanced
1What is the mathematical complexity of calculating the absolute optimal disk scheduling path (the true global minimum seek time) for a massive, arbitrary queue of random requests?
CorrectD: It is an NP-Hard problem, fundamentally equivalent to the complex Traveling Salesperson Problem
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: It is an NP-Hard problem, fundamentally equivalent to the complex Traveling Salesperson Problem
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
2How does Native Command Queuing (NCQ) completely disrupt traditional OS-level geometric disk scheduling (like SCAN)?
CorrectA: The OS sends a batch of raw requests directly to the drive, allowing the drive's internal firmware to optimize the physical head movements based on its exact, hidden internal geometry
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: The OS sends a batch of raw requests directly to the drive, allowing the drive's internal firmware to optimize the physical head movements based on its exact, hidden internal geometry
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
3What complex physical metric does the Shortest Access Time First (SATF) algorithm account for that traditional SSTF completely ignores?
CorrectB: The rotational latency required for the specific sector to spin under the head, intelligently combining both seek time and angular positioning
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: The rotational latency required for the specific sector to spin under the head, intelligently combining both seek time and angular positioning
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
4In the Linux kernel architecture, what is the primary purpose of the Completely Fair Queuing (CFQ) I/O scheduler?
CorrectC: To assign proportional I/O bandwidth to specific processes based on their assigned weight and priority, creating individual queues for each process
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: To assign proportional I/O bandwidth to specific processes based on their assigned weight and priority, creating individual queues for each process
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
5In the context of the modern Linux `kyber` I/O scheduler, how are requests intelligently dispatched to the underlying hardware?
CorrectB: By maintaining separate priority queues for synchronous reads and asynchronous writes, utilizing strict latency-based token buckets to dispatch requests
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: By maintaining separate priority queues for synchronous reads and asynchronous writes, utilizing strict latency-based token buckets to dispatch requests
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
6When an operating system utilizes Logical Volume Management (LVM) stripped over multiple physical disks, how is I/O scheduling effectively managed?
CorrectC: It maps the logical extents to physical extents and dispatches separate, independent scheduling queues to each underlying physical block device concurrently
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: It maps the logical extents to physical extents and dispatches separate, independent scheduling queues to each underlying physical block device concurrently
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
7Why is traditional cylinder-based disk scheduling becoming rapidly obsolete in enterprise solid-state NVMe environments?
CorrectD: NVMe drives possess zero mechanical moving parts and utilize thousands of parallel queues, making geometric seek optimization entirely irrelevant
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: NVMe drives possess zero mechanical moving parts and utilize thousands of parallel queues, making geometric seek optimization entirely irrelevant
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
8In a heavily fragmented traditional magnetic disk, why does the performance of the SCAN algorithm drastically degrade?
CorrectA: Because files are scattered across non-contiguous logical blocks, forcing the OS to generate dozens of separate, disjointed, full-stroke cylinder requests to read a single file
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: Because files are scattered across non-contiguous logical blocks, forcing the OS to generate dozens of separate, disjointed, full-stroke cylinder requests to read a single file
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
9What characterizes "Anticipatory Scheduling" in advanced operating systems?
CorrectC: The scheduler intentionally pauses the disk head for a few milliseconds after completing a read, anticipating that the specific application will immediately request the adjacent sector
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: The scheduler intentionally pauses the disk head for a few milliseconds after completing a read, anticipating that the specific application will immediately request the adjacent sector
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
10How does the physical phenomenon of "Zone Bit Recording" (ZBR) deeply affect advanced disk scheduling calculations?
CorrectD: Because outer cylinders physically contain more sectors than inner cylinders, the angular velocity calculations and raw transfer rates vary dramatically depending on the head's exact radial position
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: Because outer cylinders physically contain more sectors than inner cylinders, the angular velocity calculations and raw transfer rates vary dramatically depending on the head's exact radial position
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
11In high-performance Storage Area Network (SAN) environments, what is the critical function of the "Queue Depth" parameter?
CorrectA: It defines the absolute maximum number of outstanding I/O requests the host bus adapter is permitted to send to the storage controller simultaneously for firmware-level sorting
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: It defines the absolute maximum number of outstanding I/O requests the host bus adapter is permitted to send to the storage controller simultaneously for firmware-level sorting
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
12When benchmarking the effectiveness of disk scheduling algorithms, what does a high "Variance in Response Time" typically indicate?
CorrectB: That while the average throughput might be statistically acceptable, some requests are being serviced instantly while others are suffering extreme starvation
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: That while the average throughput might be statistically acceptable, some requests are being serviced instantly while others are suffering extreme starvation
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
13Which specific Linux I/O scheduler was designed to simply merge contiguous requests and implement a basic, one-way elevator without complex heuristics, making it highly ideal for Virtual Machines backed by fast SANs?
CorrectA: The `noop` (or `none`) scheduler
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: The `noop` (or `none`) scheduler
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
14In a multi-tenant cloud server utilizing `cgroups` (Control Groups), how does the "Blkio" subsystem interact with the core disk scheduler?
CorrectB: It strictly throttles IOPS and bytes-per-second limits for specific Linux containers before the I/O requests even reach the elevator queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: It strictly throttles IOPS and bytes-per-second limits for specific Linux containers before the I/O requests even reach the elevator queue
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
15If an operating system implements the VSCAN (Very Simple SCAN) algorithm, how does it typically alter the rigid C-SCAN logic?
CorrectC: It dynamically changes the scan direction based on a weighted average of pending requests, rather than strictly sweeping end-to-end
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: It dynamically changes the scan direction based on a weighted average of pending requests, rather than strictly sweeping end-to-end
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
16What is the specific mechanical penalty incurred when a disk scheduler forces a "Track-to-Track Seek" compared to a "Full-Stroke Seek"?
CorrectD: Track-to-track involves minimal head settling and acceleration time (roughly 1-2 ms), whereas a full-stroke seek requires maximum acceleration and deceleration profiles spanning the entire platter
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: Track-to-track involves minimal head settling and acceleration time (roughly 1-2 ms), whereas a full-stroke seek requires maximum acceleration and deceleration profiles spanning the entire platter
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
17How does the implementation of "Tagged Command Queuing" (TCQ) in older SCSI drives compare to modern SATA NCQ?
CorrectA: TCQ allowed the host OS to assign explicit execution priorities to tags, whereas NCQ leaves the execution ordering entirely up to the drive's internal firmware logic
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectA: TCQ allowed the host OS to assign explicit execution priorities to tags, whereas NCQ leaves the execution ordering entirely up to the drive's internal firmware logic
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
18In a clustered, distributed file system (like Ceph or GlusterFS), how does local disk scheduling occur for a single massive distributed write operation?
CorrectB: The client mathematically hashes the file object to specific placement groups, and the low-level mechanical scheduling is offloaded completely to the remote Object Storage Daemons (OSDs)
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectB: The client mathematically hashes the file object to specific placement groups, and the low-level mechanical scheduling is offloaded completely to the remote Object Storage Daemons (OSDs)
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
19What is the primary focus of the "BFQ" (Budget Fair Queuing) Linux I/O scheduler?
CorrectC: Assigning a strict time-based budget to active processes to guarantee high responsiveness for interactive tasks and smooth video playback under heavy background I/O loads
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectC: Assigning a strict time-based budget to active processes to guarantee high responsiveness for interactive tasks and smooth video playback under heavy background I/O loads
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
20What specific architectural limitation is known as the "I/O Bottleneck" in multiprocessor systems?
CorrectD: The speed of CPU and main memory advances exponentially faster than the mechanical latency of magnetic disks, causing fast processors to sit idle while waiting for disk data
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
IncorrectD: The speed of CPU and main memory advances exponentially faster than the mechanical latency of magnetic disks, causing fast processors to sit idle while waiting for disk data
This question evaluates your understanding of disk scheduling algorithms, mechanical limitations, or modern I/O scheduler implementations such as BFQ and CFQ, directly testing the core components of storage architecture.
Conclusion: Mastering Disk Scheduling Algorithms
Disk scheduling algorithms represent one of the most elegant intersections of hardware physics and software design in operating systems. These 60 MCQs have walked you through the complete spectrum — from understanding why a read/write arm’s mechanical inertia makes seek time the dominant latency factor, to appreciating how FCFS’s naive simplicity creates wild head swings, and why SSTF’s greedy local optimality sacrifices global fairness through starvation.
The elevator algorithms (SCAN, C-SCAN, LOOK, C-LOOK) solve this by enforcing structured sweeps — each a refinement of the last. Modern Linux schedulers like Deadline, BFQ, and CFQ take this further by balancing raw throughput with per-process fairness and latency guarantees. And at the frontier, NVMe’s 65,535 parallel queues have made geometric scheduling entirely obsolete for SSDs — a paradigm shift this MCQ set prepares you to reason about clearly.
Deepen your understanding with the full Disk Scheduling Algorithms theory notes , then reinforce your learning with the adjacent Disk Organization MCQs to construct a complete mental model of the OS storage stack.
📌 Key Takeaways — Disk Scheduling Algorithms
- FCFS (First Come First Served): Simplest algorithm — serves requests in arrival order. Fair but causes erratic wild head swings under mixed workloads, resulting in poor throughput.
- SSTF (Shortest Seek Time First): Greedy algorithm — always picks the closest cylinder. Maximizes throughput but causes starvation for far-away requests under heavy load.
- SCAN (Elevator Algorithm): Sweeps end-to-end, reversing at the physical disk edges. Centre tracks get serviced twice per round trip — causing mild wait-time bias.
- C-SCAN (Circular SCAN): Sweeps in one direction only, instantly jumps back to cylinder 0 without servicing. Guarantees mathematically uniform wait times across all cylinders.
- LOOK & C-LOOK: Optimized versions of SCAN/C-SCAN that reverse at the last actual request instead of the physical disk edge — eliminating unnecessary head travel.
- Deadline Scheduler (Linux): Maintains a sorted I/O queue alongside deadline-ordered queues with expiry timers (500ms reads, 5s writes) to prevent starvation while maintaining good throughput.
- BFQ (Budget Fair Queuing): Assigns time budgets to processes, guaranteeing high responsiveness for interactive tasks (video, audio) under heavy background I/O — default in many Linux distros.
- NCQ (Native Command Queuing): SATA feature that lets drive firmware reorder up to 32 queued commands internally, partially bypassing OS-level scheduling for HDDs.
- NVMe Parallel Queues: NVMe SSDs support up to 65,535 I/O queues with 65,535 commands each — making cylinder-based geometric scheduling completely irrelevant for SSDs.
- Starvation vs Fairness Trade-off: Every performance-optimized algorithm (SSTF) risks starvation; every fair algorithm (FCFS) sacrifices throughput. Modern schedulers (Deadline, BFQ) balance both.
Quick Review & Summary
Use this reference table to compare all major disk scheduling algorithms across their behaviour, performance characteristic, starvation risk, and ideal use case — perfect for rapid exam revision.
| Algorithm | Head Movement | Throughput | Starvation Risk | Best Use Case |
|---|---|---|---|---|
| FCFS | Arrival order; erratic swings | Low | None | Light loads, fair queuing |
| SSTF | Always nearest cylinder | High | High | Moderate load, no edge requests |
| SCAN | End-to-end sweep, reverses at edge | High | Low | Heavy uniform workloads |
| C-SCAN | One-way sweep, jumps to cylinder 0 | High | Very Low | Real-time / time-critical I/O |
| LOOK | Reverses at last actual request | Higher than SCAN | Low | Better SCAN replacement |
| C-LOOK | One-way; jumps to lowest request | Higher than C-SCAN | Very Low | Best classical algorithm |
| Deadline | Sorted + expiry timer override | Good | None | Linux database servers |
| CFQ | Per-process fair queues | Moderate | None | Desktop multi-process fairness |
| BFQ | Budget-based process time slices | Moderate | None | Interactive desktop / media |
| noop / none | FIFO merge only; no reorder | Maximum (SSD) | None | NVMe SSDs & virtual machines |
Frequently Asked Questions
Q. How many Disk Scheduling Algorithms MCQs are on this page?
Q. What is the difference between SCAN and LOOK disk scheduling algorithms?
Q. Why is SSTF disk scheduling algorithm prone to starvation?
Q. Why does C-SCAN provide more uniform wait times than standard SCAN?
Q. What is Native Command Queuing (NCQ) and how does it affect disk scheduling?
Q. Are disk scheduling algorithms useful for NVMe SSDs?
Q. What is the Deadline I/O scheduler and why is it used in Linux?
Q. Are these Disk Scheduling Algorithms MCQs suitable for GATE, university exams, and placement interviews?
Struggling with some questions? Re-read the full Theory Guide: Disk Scheduling Algorithms