Chapter 6: Operating Systems Fundamentals (Set-10)
In system protection, which mechanism most directly prevents a user program from executing privileged CPU instructions
A Large disk partitions
B Faster screen refresh
C User and kernel modes
D Bigger file cache
The CPU runs user programs in user mode with restricted privileges. Only the OS runs in kernel mode where privileged instructions are allowed, protecting hardware and critical memory from direct access.
When a program requests OS service using a system call, which transition happens to safely run protected code
A Cache to disk
B Trap to kernel
C Disk to RAM
D GUI to CLI
A system call triggers a controlled trap that switches execution into kernel mode. The OS performs the protected operation, then returns to user mode so the program continues safely.
In paging, which component performs address translation using page tables and protection bits
A MMU hardware
B Boot loader
C File manager
D Event logger
The Memory Management Unit translates virtual addresses into physical addresses by consulting page tables. It also enforces protection rules, preventing processes from accessing memory outside their allowed space.
Which event occurs when the needed address translation is not found in the TLB
A Page fault
B Deadlock
C TLB miss
D Warm boot
A TLB miss means the fast translation cache lacks a mapping. The CPU then consults page tables. Only if the page is absent in RAM will a page fault occur.
In demand paging, which situation directly causes a page fault
A File is hidden
B CPU is idle
C Disk is partitioned
D Page not in RAM
A page fault happens when a process accesses a virtual page not currently loaded in physical memory. The OS loads the page from disk, updates mappings, and resumes the process.
Which concept best describes the set of pages a process is actively using during a short time period
A Working set
B Boot sector
C Swap header
D Icon cache
The working set is the collection of pages frequently referenced by a process. If RAM cannot hold the working set, page faults increase sharply and performance drops due to frequent disk paging.
When a system spends most time swapping pages instead of executing processes, what is the condition called
A Spooling
B Piping
C Thrashing
D Indexing
Thrashing occurs when memory is insufficient for active processes, causing continuous page faults and heavy swapping. CPU usage becomes ineffective because the system is busy moving pages rather than doing work.
In preemptive scheduling, what mechanism commonly forces the OS to take CPU control back from a running process
A Disk cleanup
B File rename
C Window resize
D Timer interrupt
Timer interrupts occur at regular intervals and let the OS preempt the running process when its time slice ends. This ensures fairness and prevents one process from monopolizing the CPU.
Which scheduling algorithm can cause starvation for long CPU jobs if many short jobs keep arriving
A FCFS scheduling
B SJF scheduling
C Round robin
D FIFO paging
Shortest Job First always prefers shorter CPU bursts. If short tasks keep entering the queue, long tasks may wait excessively, so starvation can occur without additional fairness mechanisms.
Which scheduling approach is most directly designed for interactive systems needing fairness among users
A Round robin
B FCFS scheduling
C Batch scheduling
D Static priority
Round robin cycles through ready processes using a fixed time quantum. It gives each process CPU time regularly, improving fairness and responsiveness for interactive workloads with multiple active applications.
Which OS structure stores process state like registers and program counter for context switching
A Directory metadata
B Disk partition map
C Process control block
D Firewall rules
The PCB stores crucial process information such as state, CPU registers, program counter, scheduling data, and memory mappings. The OS uses it to save and restore processes correctly.
In concurrency, which problem occurs when thread outcomes depend on unpredictable execution timing
A Race condition
B Page fault
C Cold boot
D Disk cleanup
A race condition happens when multiple threads access shared data without proper synchronization. Different execution orders can produce different results, causing bugs that are hard to reproduce and diagnose.
Which mechanism ensures only one thread enters a critical section at any time
A Spooling queue
B Paging table
C Mutual exclusion
D Boot manager
Mutual exclusion uses locks or mutexes to prevent concurrent access to shared critical resources. It ensures consistency by letting only one thread modify shared data at a time.
Which deadlock condition means a process holds one resource while waiting for another
A Full preemption
B Hold and wait
C No sharing
D Shortest job
Hold and wait occurs when a process keeps already allocated resources while requesting additional ones. This can form waiting chains that contribute to deadlocks when combined with other conditions.
Which deadlock condition means a resource cannot be forcibly taken from a process
A No preemption
B Full sharing
C Infinite resources
D Always release
No preemption means resources are released only voluntarily by the holding process. If the OS cannot reclaim resources to break a wait chain, deadlocks become possible.
Which deadlock condition creates a closed waiting loop among processes
A Ready state
B Time slicing
C Circular wait
D Page replacement
Circular wait happens when each process waits for a resource held by another process in a cycle. This closed chain prevents progress, causing processes to remain blocked indefinitely.
Which algorithm prevents deadlock by granting requests only if the system remains in a safe state
A Round robin
B Banker’s algorithm
C FIFO queue
D Disk caching
Banker’s algorithm checks whether allocating resources would keep the system in a safe state where all processes can finish. Unsafe requests are delayed, preventing deadlock in resource allocation.
In segmentation, what is the main reason external fragmentation can occur
A Fixed page sizes
B TLB caching
C CPU time slicing
D Variable segment sizes
Segments have variable sizes based on program structure. As segments are allocated and freed, scattered holes form in memory, making it difficult to allocate large contiguous segments even with enough total free memory.
Which register pair checks that a process accesses only its valid memory range
A Base and limit
B TLB and MMU
C BIOS and UEFI
D GUI and CLI
Base defines the starting address of a process region and limit defines its size. The CPU checks each memory access against these to block illegal references outside the allowed range.
In Unix-like systems, what does the setuid bit on an executable primarily do
A Hide file name
B Encrypt file data
C Run as owner
D Resize partitions
Setuid causes an executable to run with the file owner’s privileges, often root. It allows controlled privileged actions, but insecure setuid programs can be exploited, so they must be carefully designed.
Which permission combination typically allows listing directory entries and accessing items within
A Write only
B Read and execute
C Execute only
D Read only
Read permission allows listing names in a directory, and execute permission allows traversal and access to items. Without execute, you cannot reach files; without read, you cannot list entries.
Which mechanism prevents two processes from writing conflicting updates to the same file simultaneously
A File renaming
B File indexing
C File locking
D File preview
File locking controls concurrent access to a file, ensuring only permitted operations occur at a time. It prevents corruption and inconsistent updates, especially for shared documents and databases.
Which file system feature improves recovery by logging operations before final commit
A Journaling
B Piping output
C Spooling jobs
D Aging priority
Journaling writes a log of intended file system changes. After a crash, the OS uses the journal to replay or roll back updates, restoring consistent metadata and reducing corruption risk.
Which caching method increases risk of data loss if power fails before data is written to disk
A Write-through caching
B Read-only caching
C No caching
D Write-back caching
Write-back caching stores updates in memory and writes them to disk later for speed. If power fails before flushing buffers, recent changes may be lost or the file system may become inconsistent.
Which operation forces cached writes to be committed to storage for safety
A Raise priority
B Flush buffers
C Disable paging
D Stop services
Flushing buffers writes cached data from memory to disk immediately. It reduces corruption and data loss risk during shutdown or power failure by ensuring changes are physically stored.
On BIOS systems, which structure contains initial boot code and partition table in first sector
A Page directory
B Swap partition
C Master Boot Record
D Registry hive
The MBR is the first sector on a boot disk in BIOS systems. It contains bootstrapping code and partition info so the system can find the active partition and continue booting.
In UEFI systems, which feature blocks unauthorized boot loaders using digital signatures
A Secure Boot
B Fast Startup
C Safe Mode
D System Restore
Secure Boot verifies signatures of boot components and allows only trusted code at startup. It helps prevent bootkits and other malware that attempts to load before the OS security tools start.
Which Windows tool is best for long-term analysis of CPU, disk queue, and memory counters
A Task Manager
B Disk Cleanup
C Performance Monitor
D File Explorer
Performance Monitor collects and graphs detailed system counters over time. It helps diagnose bottlenecks, compare trends, and validate whether configuration changes improved performance beyond short snapshots.
Which Windows tool is most useful to investigate repeated service crashes using error logs and event IDs
A Device Manager
B Event Viewer
C Disk Management
D Control Panel
Event Viewer stores system and application logs with event IDs and timestamps. It helps identify failing services, drivers, or components and supports targeted fixes based on recorded error details.
Which OS control decides whether a background service starts automatically at boot or manually later
A Page size choice
B Disk cluster size
C Window theme
D Service startup type
Service startup type controls if a service runs at boot, starts on demand, or stays disabled. Correct configuration improves performance and security by preventing unnecessary services from running.
In OS security, what does authentication verify during login
A Disk free space
B CPU speed
C User identity
D Screen layout
Authentication confirms who a user is using passwords, keys, or biometrics. After identity is verified, authorization then decides what resources and actions the user is allowed to access.
In OS security, what does authorization decide after a successful login
A Allowed permissions
B Boot device order
C File compression level
D Monitor resolution
Authorization checks what the authenticated user can do, such as reading files, installing software, or changing settings. It enforces access control policies using roles, groups, and permissions.
Which access control model assigns permissions based on job roles like “admin” or “operator”
A Discretionary access
B Random access
C Open access
D Role-based access
RBAC assigns permissions to roles rather than individuals. Users gain permissions by membership in roles, simplifying management and improving consistency across large organizations with many accounts.
Which OS technique lets one command’s output become another command’s input in a shell
A Paging memory
B Patching OS
C Piping output
D Spooling prints
Piping chains commands so the output of one program becomes input for another. It is powerful for filtering logs, searching text, and building automated command workflows efficiently.
Which I/O feature transfers data between device and RAM with minimal CPU copying
A DMA transfer
B Manual polling
C GUI buffering
D File locking
DMA allows devices to read or write memory directly after setup, reducing CPU involvement. This improves performance for high-speed I/O like disks and network adapters while freeing CPU for other work.
Why is interrupt-driven I/O generally better than polling for CPU efficiency
A Increases disk size
B Improves icon quality
C Avoids busy waiting
D Reduces file names
With interrupts, devices signal the CPU when they need service. The CPU can do other work instead of repeatedly checking device status, improving overall system efficiency and responsiveness.
Which OS component is mainly responsible for managing multiple virtual machines on one host
A Boot loader
B File explorer
C Text editor
D Hypervisor
The hypervisor allocates CPU, memory, storage, and devices to guest OS instances. It schedules and isolates virtual machines so multiple systems can run safely on the same physical hardware.
Which hypervisor type runs directly on hardware and is common in enterprise servers
A Type 2 hypervisor
B Type 1 hypervisor
C Shell program
D Device driver
Type 1 hypervisors run on bare metal without a host OS, offering stronger isolation and better performance. They are widely used in data centers to host many virtual servers reliably.
Which hypervisor type runs as a program on an existing OS, common for personal testing
A Type 1 hypervisor
B Kernel firmware
C Type 2 hypervisor
D Disk controller
Type 2 hypervisors depend on a host OS and run like normal applications. They are easier to install for learning, but typically have more overhead than Type 1 solutions.
Which scheduling metric measures time from submitting a job until it finishes completely
A Turnaround time
B Response time
C Idle time
D Boot time
Turnaround time includes waiting, running, and I/O time from job submission to completion. It is a key metric for batch workloads, reflecting how long users wait for results overall.
Which scheduling metric measures how quickly the system first responds to a user action
A Turnaround time
B Disk time
C Cache time
D Response time
Response time is the time until a system first produces output after user input. Lower response time improves perceived performance, especially for interactive tasks like typing, clicks, and UI actions.
Why is preemptive multitasking more robust than cooperative multitasking against frozen apps
A Disk never fills
B Files auto compress
C OS regains control
D Icons auto sort
In preemptive multitasking, the OS can interrupt a misbehaving process and schedule others. Cooperative systems rely on programs to yield CPU, so one frozen app can block the entire system.
Which disk metric indicates many pending I/O requests waiting to be served by the disk
A Disk queue length
B Screen refresh rate
C CPU voltage
D RAM size
Disk queue length shows how many read/write requests are waiting. High queue length often indicates a disk bottleneck, causing slow file operations and application delays under heavy I/O load.
Which patching practice reduces widespread failures by testing updates on a small group first
A Random rollout
B Staged rollout
C Disable updates
D Force all updates
Staged rollout deploys patches gradually, starting with a pilot group. If issues appear, deployment can stop before affecting everyone, improving reliability in organizations with many systems.
Which Windows database stores many system and application configuration settings centrally
A Swap space
B Page table
C Boot record
D Registry database
The Registry stores configuration settings for hardware, OS components, users, and apps. Because it is central, incorrect changes can cause system problems, so it is managed via trusted tools.
Which OS mechanism queues print jobs so applications are not blocked by slow printing
A Memory paging
B Disk mirroring
C Print spooling
D File locking
Spooling stores print jobs in a queue and sends them to the printer one by one. It prevents conflicts in shared printing and allows users to continue working while printing runs.
Which mechanism uses temporary memory areas to smooth speed differences during device input/output
A Buffering
B Aging
C Booting
D Logging
Buffering holds data temporarily during I/O transfers. It helps match fast CPU processing with slower devices like disks and networks, reducing waiting and improving data flow consistency.
Which recovery step is most direct if a newly installed driver causes repeated crashes
A Increase page size
B Roll back driver
C Defragment disk
D Change user theme
Driver rollback restores the previous working driver version. It quickly reverses a faulty driver update, often fixing crashes or device failures without requiring a full OS reinstall.
Why is using a standard user account safer for daily work than using an admin account
A Increases CPU speed
B Expands disk space
C Limits damage scope
D Improves graphics
Standard accounts have limited privileges, so malware or mistakes cannot easily change system-wide settings or protected files. Admin rights are used only when necessary, improving overall system security.
In distributed systems, what approach keeps a service available when one node fails
A Replication and failover
B Disk cleanup cycle
C Icon arrangement
D Window snapping
Replication keeps copies of data or services on multiple nodes. Failover shifts work to a healthy node if one fails, improving availability, reliability, and continuity for users in distributed environments.