D686 Operating Systems for Computer Scientists - Set 3 - Part 1

Correct Answer: Selective suspension

Selective suspension maintains essential services while stopping non-critical processes, balancing functionality with power conservation to extend battery life during low power conditions.
Option a is incorrect because complete shutdown terminates all processes including critical system functions, making the device unusable rather than extending operation time.
Option c is incorrect because full throttling reduces all processing speeds uniformly, potentially affecting critical functions needed for basic device operation and usability.
Option d is incorrect because random termination could stop critical processes while leaving non-essential ones running, causing system instability and unpredictable behavior patterns.

Correct Answer: Snapshot creation

Snapshots capture complete system state instantly at specific times, enabling point-in-time recovery without the overhead of continuous data recording or synchronization processes.
Option a is incorrect because incremental backups save only changes since last backup, requiring multiple restores to reach specific points in time accurately.
Option c is incorrect because mirror synchronization maintains real-time copies continuously, consuming resources constantly rather than capturing discrete point-in-time states efficiently.
Option d is incorrect because journal replay reconstructs state from logged operations, not directly capturing complete system state at specific moments instantly.

Correct Answer: Resource quotas

Resource quotas set per-user limits on CPU, memory, and storage usage, preventing monopolization while ensuring fair distribution among all system users effectively.
Option a is incorrect because priority inheritance addresses priority inversion in real-time systems, not general resource distribution fairness among multiple users comprehensively.
Option c is incorrect because random allocation doesn't guarantee fairness or prevent monopolization, potentially giving excessive resources to some users randomly selected.
Option d is incorrect because first-come service can allow early users to consume all resources, preventing fair access for later arriving users.

Correct Answer: Two-phase commit

Two-phase commit protocol coordinates distributed transactions through prepare and commit phases, ensuring atomicity across multiple resources or systems participating in transactions.
Option a is incorrect because checkpointing saves system state periodically for recovery but doesn't ensure transaction atomicity across distributed resources or systems.
Option b is incorrect because transaction logs record operations for recovery but don't directly enforce all-or-nothing execution semantics for atomic transactions fundamentally.
Option d is incorrect because write-ahead logging ensures durability by logging before writing data, not specifically enforcing atomic transaction completion across resources.

Correct Answer: Memory fence

Memory fences prevent instruction reordering across barrier points, ensuring memory operations complete in program order necessary for correct concurrent execution behavior.
Option a is incorrect because cache flush writes cached data to memory but doesn't prevent instruction reordering by CPU or compiler optimizations applied.
Option c is incorrect because pipeline stalls pause instruction execution temporarily but don't specifically prevent memory operation reordering across synchronization points needed.
Option d is incorrect because branch prediction optimizes conditional execution flow, unrelated to memory ordering constraints in concurrent programming synchronization requirements fundamentally.

Correct Answer: Vsync synchronization

Vsync synchronization aligns frame rendering with display refresh rates, preventing screen tearing and ensuring smooth visual presentation at consistent intervals during gameplay.
Option a is incorrect because deadline scheduling handles general real-time tasks but doesn't specifically synchronize with display hardware refresh timing for graphics.
Option c is incorrect because priority boosting elevates process importance temporarily but doesn't guarantee frame completion aligned with display refresh cycles specifically needed.
Option d is incorrect because batch processing groups operations for efficiency, inappropriate for real-time graphics rendering requiring consistent frame delivery timing.

Correct Answer: Audit logs

Audit logs chronologically record system events, user activities, and security-relevant operations, providing essential forensic evidence for incident investigation and compliance requirements.
Option a is incorrect because process tables track running processes and their state, not maintaining historical records of system events for forensic analysis.
Option c is incorrect because page tables map virtual to physical memory addresses, not recording user actions or security events for investigation purposes.
Option d is incorrect because file cache improves file access performance by buffering data, not maintaining security event records for forensic examination.

Correct Answer: Guaranteed deadlines

Hard real-time systems guarantee task completion within specified deadlines, critical for safety systems where timing violations could cause catastrophic failures or injuries.
Option a is incorrect because boot time affects system startup but doesn't ensure deterministic behavior during operation critical for safety system responses.
Option c is incorrect because memory efficiency is beneficial but doesn't provide the timing guarantees essential for safety-critical automotive control systems fundamentally.
Option d is incorrect because interface simplicity aids usability but doesn't ensure the deterministic timing required for brake and airbag system reliability.

Correct Answer: Process isolation

Process isolation places each tab in separate processes with independent address spaces, preventing cross-tab access even if one tab is compromised.
Option a is incorrect because code signing verifies software authenticity but doesn't provide runtime isolation between different web content in browser tabs.
Option c is incorrect because stack canaries detect buffer overflows in individual processes but don't isolate tabs from each other fundamentally required.
Option d is incorrect because input validation sanitizes data but doesn't provide address space separation needed for tab isolation security model implementation.

Correct Answer: Master-slave replication

Master-slave replication directs writes to master node which propagates changes to slaves, allowing fast local reads while maintaining consistency through controlled updates.
Option a is incorrect because read-write splitting routes operations but doesn't define how consistency is maintained across distributed database replicas geographically separated.
Option c is incorrect because peer-to-peer synchronization can cause conflicts when multiple nodes accept writes simultaneously without clear authority for resolution.
Option d is incorrect because centralized locking would require remote coordination for all operations, eliminating the performance benefit of local reads entirely.

Correct Answer: Linux namespaces

Linux namespaces isolate process groups with independent views of system resources, enabling container isolation without full virtualization overhead of separate kernels.
Option a is incorrect because control groups limit resource usage but don't provide the view isolation that namespaces create for containerized processes fundamentally.
Option c is incorrect because security modules enforce access policies but don't create isolated resource views that define container boundaries and separation.
Option d is incorrect because kernel capabilities provide fine-grained privileges but don't isolate system resource views between different container instances running concurrently.

Correct Answer: Multi-channel memory

Multi-channel memory architectures provide parallel paths to memory banks, multiplying bandwidth by allowing simultaneous access through independent channels for performance improvement.
Option a is incorrect because virtual memory provides address space abstraction and disk-based extension, not specifically increasing memory bandwidth for parallel access patterns.
Option c is incorrect because shared memory refers to inter-process communication mechanisms, not the physical memory architecture for bandwidth improvement specifically needed.
Option d is incorrect because cache memory reduces latency for frequently accessed data but doesn't increase main memory bandwidth for large data transfers.

Correct Answer: Copy-on-write clones

Copy-on-write clones create instant copies sharing original data blocks, only allocating new blocks when modifications occur, enabling efficient version tracking.
Option a is incorrect because hard links create additional directory entries to same file data, not providing versioning when original file is modified.
Option c is incorrect because symbolic links are pointers to file paths, not creating actual copies or versions of file data for tracking.
Option d is incorrect because extended attributes store metadata about files but don't provide versioning or copy functionality for tracking modifications efficiently.

Correct Answer: Batch scheduling

Batch scheduling runs processes to completion without preemption, eliminating context switch overhead ideal for computation-intensive mining tasks requiring maximum throughput achievable.
Option a is incorrect because interactive priority optimizes response time through frequent switching, reducing throughput for computation-intensive batch workloads like mining operations.
Option c is incorrect because real-time priority ensures deadline compliance with preemption, adding overhead unnecessary for mining computations without timing constraints present.
Option d is incorrect because fair sharing divides resources equally requiring switches between users, reducing efficiency for homogeneous computation tasks in mining.

Correct Answer: Volume snapshots

Volume snapshots automatically preserve file system state at intervals, enabling recovery of pre-encryption versions without relying on user-initiated backups or interventions.
Option a is incorrect because file compression reduces storage space but doesn't maintain previous versions for recovery after ransomware encryption attacks occur.
Option c is incorrect because disk quotas limit user storage consumption but don't provide version history for recovering from encryption attacks effectively.
Option d is incorrect because access logs record file operations but don't preserve actual file contents needed for recovery after encryption happens.

Correct Answer: Resource constraints

Edge systems operate with limited CPU, memory, and power compared to cloud data centers, requiring optimized operating systems for constrained environments effectively.
Option a is incorrect because while storage differs, the fundamental distinction is overall resource limitations not just storage capacity at edge locations.
Option c is incorrect because network speed varies in both environments; edge computing's advantage is proximity not necessarily network speed to endpoints.
Option d is incorrect because user interfaces depend on use case not location; edge systems may be headless or have interfaces like cloud systems.

Correct Answer: Rounding inconsistency

Floating-point operations aren't associative due to rounding, causing different execution orders in parallel threads to produce slightly different numerical results unexpectedly.
Option a is incorrect because integer overflow involves exceeding integer representation limits, not the ordering sensitivity of floating-point operations in parallel execution.
Option c is incorrect because memory corruption involves invalid memory access or modification, not numerical precision issues from operation ordering in calculations.
Option d is incorrect because cache thrashing involves repeated cache misses from competing access patterns, not floating-point calculation precision issues fundamentally occurring.

Correct Answer: Socket layer

Socket layer encryption (like TLS) secures data before network transmission, providing transparent encryption to applications while protecting data in transit effectively.
Option a is incorrect because application layer encryption requires each application to implement crypto, not providing system-wide transparent encryption for connections universally.
Option c is incorrect because device drivers handle hardware communication but encryption typically occurs at higher layers for flexibility and standardization needed.
Option d is incorrect because physical layer involves electrical signals on wires, too low level for practical encryption implementation and key management.

Correct Answer: Memory pre-copy

Memory pre-copy iteratively copies memory pages while VM runs, minimizing downtime to milliseconds during final synchronization, preserving connections throughout migration process.
Option a is incorrect because cold migration requires shutting down the VM completely, disrupting all active connections and causing noticeable service interruption unavoidably.
Option c is incorrect because suspend and resume stops VM execution temporarily, breaking active network connections that timeout during the suspension period.
Option d is incorrect because checkpoint restart saves and restores VM state but involves stopping and starting, disrupting continuous operation and connections.

Correct Answer: Network services

Network services like SSH or web interfaces enable remote management of headless devices, providing full control without local input/output hardware requirements present.
Option a is incorrect because serial console requires physical cable connection and terminal, not truly remote and still needs some local access capability.
Option c is incorrect because voice commands require microphones and processing power often unavailable in resource-constrained headless IoT devices typically deployed widely.
Option d is incorrect because touch interfaces need displays and touch sensors, contradicting the headless nature of devices lacking traditional input methods fundamentally.