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

Correct Answer: Storage area network

SAN provides dedicated high-speed networks for block-level storage access, separating storage traffic from regular network traffic for optimal performance and reliability.
Option a is incorrect because host-attached storage connects directly to servers through SATA or SAS, not over networks, limiting sharing capabilities significantly.
Option b is incorrect because NAS provides file-level access over regular network infrastructure, not block-level access on dedicated storage networks like SAN.
Option d is incorrect because cloud storage typically uses internet protocols and APIs for access, not dedicated networks with block-level storage protocols.

Correct Answer: Cannot be disabled

Non-maskable interrupts cannot be disabled by software and must be serviced immediately, typically reserved for critical hardware errors requiring immediate attention.
Option a is incorrect because while NMIs have high priority, their defining feature is being non-disableable rather than just priority level alone.
Option c is incorrect because processing speed depends on handler implementation; NMIs are distinguished by mandatory handling, not necessarily faster execution time.
Option d is incorrect because NMIs are typically hardware-generated for critical events; software generates regular interrupts through system calls or traps.

Correct Answer: Password and biometric

Combining something you know with something you are provides strong authentication by requiring both knowledge and physical presence for system access.
Option a is incorrect because two passwords both represent knowledge factors, not providing true two-factor authentication with different factor types for security.
Option c is incorrect because two biometrics represent the same factor type, less secure than combining different factor categories for authentication strength.
Option d is incorrect because username isn't an authentication factor but an identifier; this represents single-factor authentication with only password protection.

Correct Answer: Parent reads status

Parent process must call wait to read child's exit status, allowing OS to remove zombie entry and free process table slot completely.
Option a is incorrect because zombie processes already released memory and resources; they only retain process table entry awaiting parent status collection.
Option c is incorrect because system reboot unnecessarily disrupts all processes when simple parent wait call would properly clean up zombie processes.
Option d is incorrect because zombies don't timeout automatically; they persist until parent collects status or parent terminates causing init adoption.

Correct Answer: Approaches minimum

Higher TLB hit ratios reduce page table lookups, making effective access time approach the faster TLB access time plus single memory access.
Option a is incorrect because increased hit ratio means fewer slow page table walks, decreasing rather than increasing overall access time significantly.
Option b is incorrect because effective access time varies with hit ratio; it's weighted average of hit and miss cases, not constant value.
Option d is incorrect because the relationship is predictable and deterministic based on hit ratio, TLB access time, and memory access time parameters.

Correct Answer: Unbounded delays

Priority inversion causes high-priority tasks to wait indefinitely when medium-priority tasks preempt low-priority tasks holding required resources, violating timing guarantees.
Option a is incorrect because priority inversion involves waiting for resource release, not circular dependencies between multiple processes required for deadlock.
Option c is incorrect because resource starvation typically affects low-priority tasks; priority inversion specifically impacts high-priority task scheduling and timing.
Option d is incorrect because context thrashing involves excessive switching between processes, different from priority-based resource waiting delays in priority inversion.

Correct Answer: Metadata changes

Journals record metadata modifications like directory updates and allocation changes, allowing file system consistency restoration after crashes without full file system checks.
Option a is incorrect because journaling typically tracks structural changes, not actual file data contents which would require excessive storage space overhead.
Option c is incorrect because user passwords are authentication data stored separately, not file system structural information needing crash recovery protection through journaling.
Option d is incorrect because network packets are transient communication data unrelated to persistent file system structure and metadata consistency maintenance requirements.

Correct Answer: Processor affinity

Processor affinity binds processes to specific cores, maintaining cache locality and reducing cache misses from migration between different cores' caches repeatedly.
Option a is incorrect because load balancing distributes work across cores for utilization, potentially moving processes and invalidating their cached data frequently.
Option c is incorrect because gang scheduling coordinates related thread scheduling together, not keeping individual processes on the same cores for cache benefits.
Option d is incorrect because fair scheduling ensures equal CPU time distribution among processes, unrelated to cache optimization through core assignment persistence.

Correct Answer: Page fault

Page fault exception occurs when accessing non-resident pages, triggering OS handler to locate, load, and map the page before resuming execution.
Option a is incorrect because process creation doesn't immediately load all pages; demand paging delays loading until pages are actually referenced during execution.
Option c is incorrect because cache misses involve CPU cache and main memory, not the virtual memory page loading from secondary storage mechanism.
Option d is incorrect because buffer overflow is a security vulnerability from boundary checking failures, unrelated to demand paging page loading triggers.

Correct Answer: Encryption at all layers

Encrypting data at rest, in transit, and in processing provides multiple protection barriers, ensuring security even if one layer is compromised.
Option a is incorrect because multiple passwords address only authentication, not providing comprehensive protection against various attack vectors throughout system architecture comprehensively.
Option c is incorrect because single firewall creates single point of failure; defense in depth requires multiple different security mechanisms working together collaboratively.
Option d is incorrect because backups help recovery after attacks but don't prevent breaches; comprehensive security requires active protection mechanisms at multiple levels.