In protected-mode systems, why must user programs use system calls for tasks like opening hardware devices
A Faster screen drawing
B Larger disk space
C Privileged access control
D Better icon layout
Hardware access is restricted to kernel mode for safety. System calls provide a controlled entry so the OS can validate requests, enforce permissions, and prevent user programs from damaging devices or memory.
When a process triggers a trap to request an OS service, what CPU mode change typically occurs
A Kernel to user
B User to kernel
C RAM to disk
D Disk to RAM
A trap or system call switches execution to kernel mode so protected operations can run. After the OS finishes the service, it returns control to user mode to continue the program safely.
In virtual memory, which structure stores virtual-to-physical page mappings for a process
A Boot record
B Log file
C Icon cache
D Page table
A page table contains entries mapping virtual pages to physical frames with permission bits. The MMU consults it to translate addresses, protect memory, and support isolated address spaces for processes.
Which fast hardware cache reduces repeated page-table lookups during address translation
A FAT table
B MBR record
C TLB cache
D Swap file
The Translation Lookaside Buffer stores recent address translations. When a mapping is found in the TLB, translation is faster. A miss forces lookup in page tables, increasing memory access cost.
What does a page fault specifically indicate in a demand-paged system
A Page not in RAM
B Disk physically failed
C CPU overheated
D File permission denied
A page fault occurs when a process accesses a virtual page not currently loaded in physical memory. The OS pauses the process, loads the page from disk, updates tables, then resumes.
Which condition best describes “thrashing” in a system using virtual memory
A Too many icons
B Low screen refresh
C Excessive page swapping
D Wrong keyboard layout
Thrashing happens when the OS spends most time swapping pages between RAM and disk instead of running processes. It usually occurs when too many active processes compete for limited memory.
In CPU scheduling, which method can starve long jobs if short jobs keep arriving frequently
A FCFS scheduling
B Round robin
C Lottery scheduling
D Shortest job first
Shortest job first always chooses the smallest estimated CPU burst. If short jobs keep coming, long jobs may wait a very long time. Preemptive variants can worsen this without safeguards.
Which scheduling approach is most directly associated with a fixed time quantum per process
A FCFS scheduling
B Batch scheduling
C Round robin
D Deadline scheduling
Round robin assigns each ready process a time slice. When the quantum ends, the OS preempts the process and moves to the next. This improves fairness and interactive responsiveness.
In preemptive multitasking, which event most commonly forces the OS to switch processes
A Screen resize
B Timer interrupt
C File rename
D Icon click
A periodic timer interrupt lets the OS regain control to enforce time slices. It enables fair CPU sharing and prevents one process from running forever, even if it never performs I/O.
Which OS data structure stores registers and state needed to resume a paused process correctly
A Process control block
B Directory entry
C Boot sector
D Firewall rule
The PCB holds critical process info like state, program counter, registers, scheduling data, and memory pointers. During context switching, the OS saves and restores state using the PCB.
Which concept ensures only one thread enters a critical section at a time
A Disk caching
B Fast booting
C Mutual exclusion
D File indexing
Mutual exclusion prevents concurrent access to shared data. Using mutexes or locks, the OS or runtime ensures only one thread can modify critical resources at a time, avoiding race conditions.
In deadlock theory, which required condition means a resource cannot be shared simultaneously
A Preemption allowed
B No waiting
C Infinite resources
D Mutual exclusion
Deadlock needs mutual exclusion, meaning some resources are non-shareable. If a resource can be used by only one process at a time, processes can end up waiting forever for each other.
Which deadlock condition means a process holds one resource while waiting to acquire another
A Hold and wait
B No circularity
C Full preemption
D Early release
Hold and wait occurs when a process keeps currently held resources while requesting more. This can create chains of waiting processes, contributing to deadlock when combined with other conditions.
Which deadlock condition means resources cannot be forcibly taken away by the OS
A Full sharing
B Low priority
C No preemption
D Fast scheduling
No preemption means a resource must be released voluntarily by the holding process. If the OS cannot take back resources to break wait chains, deadlocks become possible in resource allocation.
Which deadlock condition creates a closed loop of processes each waiting for another’s resource
A Short job first
B Circular wait
C Time slicing
D Paging method
Circular wait exists when process A waits for a resource held by B, B waits for C, and so on until a process waits for A. This closed chain can freeze all involved processes.
Which algorithm checks safe states before granting resource requests to avoid deadlock
A FIFO paging
B FCFS scheduling
C Banker’s algorithm
D FAT allocation
Banker’s algorithm simulates allocation to see if the system stays in a safe state. If granting a request could lead to unsafe states, the OS delays it, preventing deadlock.
In segmentation, what is the main unit that matches program structure like code, data, and stack
A Segment
B Page frame
C Disk sector
D File cluster
Segmentation divides memory into logical segments such as code, data, and stack. Each segment has its own base and limit, making memory organization closer to program structure than paging.
Compared with paging, segmentation is more likely to suffer from which memory problem
A TLB misses
B Page faults
C External fragmentation
D Internal locking
Segments are variable-sized, so free gaps appear as programs allocate and release memory. Over time, scattered holes can prevent allocating a large segment even if total free memory is enough.
Which memory register pair helps enforce bounds checking for a process’s address space
A FAT and NTFS
B BIOS and UEFI
C GUI and CLI
D Base and limit
Base holds the starting physical address, and limit holds the size of the allowed range. The CPU checks every memory reference, blocking accesses outside the process’s permitted region.
In Unix-like systems, what do setuid permissions mainly allow when applied to an executable
A Hide from listing
B Run as file owner
C Reduce disk usage
D Change screen theme
Setuid makes an executable run with the file owner’s privileges, often root. It enables controlled privileged tasks, but must be used carefully because security bugs can be exploited.
Which file system feature logs updates so metadata remains consistent after crashes
A Mirroring
B Stripping
C Journaling
D Caching
Journaling records intended file system changes before committing them fully. After a crash, the OS can replay the journal to restore consistency, reducing corruption and speeding recovery.
When a disk uses write-back caching, what risk increases if power fails suddenly
A Unwritten data loss
B Faster booting
C Larger partitions
D Better permissions
Write-back caching delays writing changes to disk for speed. If power fails before buffers are flushed, recent changes may be lost or file system metadata can become inconsistent.
Which mechanism ensures buffered writes are committed to storage before shutdown completes
A Increase time quantum
B Disable paging
C Flush disk buffers
D Stop GUI shell
Flushing forces cached data in memory to be written to disk. This reduces corruption risk by ensuring recent updates are committed before power-off, especially important for file system integrity.
On BIOS systems, which structure contains initial boot code in the first disk sector
A Page directory
B Swap partition
C Event database
D Master Boot Record
The MBR contains bootstrapping code and a partition table. BIOS loads this first sector into memory and executes it to locate the active partition or next boot stage.
In UEFI boot, what is the key security feature that blocks unsigned boot loaders
A Fast Startup
B Safe Mode
C Secure Boot
D System Restore
Secure Boot verifies digital signatures of boot components and allows only trusted boot loaders. This helps prevent bootkits and rootkits that attack the system before the OS fully loads.
Which Windows tool is most suitable to view long-term trends using CPU, disk queue, and memory counters
A Task Manager
B Performance Monitor
C File Explorer
D Disk Cleanup
Performance Monitor collects detailed counters over time, allowing analysis of bottlenecks and trends. It is better than snapshots because it shows how resource usage changes during normal workloads.
Which tool is best for diagnosing repeated driver failures by reading time-stamped system error logs
A Event Viewer
B Disk Management
C Control Panel
D Paint app
Event Viewer records system events, warnings, and errors with details and timestamps. Driver failures, service crashes, and boot errors appear here, helping identify the root cause accurately.
If an OS uses RBAC, how are permissions typically assigned in the simplest correct way
A Through file names
B Through screen themes
C Through user roles
D Through disk size
Role-based access control assigns permissions to roles like admin, operator, or user. People get permissions by being placed into roles, simplifying security management and making access consistent.
Which OS interface technique lets command output become input for another command in a shell
A Paging memory
B Spooling print
C Patching OS
D Piping output
Piping connects commands so one command’s output feeds another’s input. It enables powerful text processing and automation, such as filtering logs, searching patterns, and chaining utilities efficiently.
In device I/O, what does DMA mainly allow without heavy CPU involvement
A Faster screen redraw
B Safer password login
C Direct memory transfer
D Larger directory list
Direct Memory Access lets devices transfer data to or from RAM without continuous CPU copying. The CPU sets up the transfer, and the device handles movement, improving throughput and freeing CPU time.
Why is interrupt-driven I/O generally more efficient than constant polling
A CPU avoids busy waiting
B Disk gets larger
C GUI becomes faster
D Files become smaller
With interrupts, devices notify the CPU only when service is needed, so the CPU can do other work meanwhile. Polling wastes CPU time by repeatedly checking device status.
Which tool helps manage background services and change startup type to Manual or Disabled
A Disk Cleanup
B File Explorer
C Services console
D Screen reader
The Services console lists system services and allows start, stop, and configuration. Changing startup type controls whether a service runs at boot, on demand, or never, affecting performance and features.
Which OS concept best explains why one user cannot read another user’s protected files
A Disk partitioning
B Access permissions
C Window snapping
D Screen scaling
File permissions restrict who can read, write, or execute files. Combined with ownership and groups, they enforce access control so users cannot open protected data without authorization.
In Unix-like systems, which permission is essential to traverse a directory path even if you know filenames
A Read on directory
B Write on directory
C Execute on directory
D Hidden attribute
Execute permission on a directory allows traversal, meaning you can enter and access items inside. Without it, you cannot reach files, even if you know their names, because path access is blocked.
In Windows, what is the main purpose of NTFS ACLs compared to simple attributes
A Fine-grained permissions
B Faster boot time
C Larger icons
D Better sound
NTFS Access Control Lists define detailed permissions for users and groups, like read, write, modify, and full control. They provide stronger security than simple read-only or hidden attributes.
Which OS feature helps ensure one application crash usually does not crash the whole system
A Disk formatting
B File journaling
C Process isolation
D GUI theming
Process isolation separates memory and resources per process. If an app crashes, the OS can terminate it without affecting other processes, keeping the system stable and continuing other tasks normally.
In virtualization, what does a hypervisor mainly do
A Replace device drivers
B Encrypt user files
C Clean disk space
D Manage virtual machines
A hypervisor creates and manages virtual machines by allocating CPU, memory, storage, and devices. It provides isolation and scheduling so multiple guest OS instances can run on one host.
Which hypervisor type runs directly on hardware and is common in server virtualization
A Type 2 hypervisor
B Batch controller
C Type 1 hypervisor
D Boot manager
Type 1 hypervisors run on bare metal without a host OS, offering better performance and isolation. They are widely used in data centers to run many virtual machines efficiently.
Which hypervisor type runs as an application on top of an existing OS, common for desktop testing
A Type 2 hypervisor
B Type 1 hypervisor
C Firmware loader
D Kernel module
Type 2 hypervisors run inside a host operating system. They are easy to install for learning and testing, but add overhead because hardware access is mediated by the host OS.
Which scheduling measure improves user experience by reducing how long interactive tasks wait to run
A Disk space
B File size
C Response time
D Screen contrast
Response time measures how quickly a system reacts to user input. Scheduling policies aim to reduce it for interactive tasks by giving CPU time promptly, improving perceived speed and smoothness.
In CPU scheduling, what does turnaround time measure for a process
A Boot to shutdown
B Login to logout
C Read to write
D Submit to completion
Turnaround time is the total time from when a process is submitted to when it finishes. It includes waiting, running, and I/O time, and is key for measuring batch workload efficiency.
In OS design, why is preemptive multitasking safer than cooperative multitasking for stability
A Files are always smaller
B Disk never fills
C OS can regain control
D GUI never freezes
In preemptive multitasking, the OS can stop a misbehaving process and schedule others. Cooperative systems rely on programs yielding CPU, so one faulty app can freeze the entire system.
Which disk metric in performance analysis indicates requests are waiting because the disk is overloaded
A Screen refresh rate
B Disk queue length
C CPU voltage
D Keyboard latency
Disk queue length shows how many I/O requests are waiting. High values often indicate disk bottlenecks, causing slow file operations and increased application delays, especially under heavy workload.
Which OS update approach reduces large-scale failures by testing patches on a small group first
A Staged rollout
B Random install
C Disable updates
D Manual guessing
Staged rollout deploys updates gradually, first to a limited set of systems. If problems appear, deployment can be paused, reducing risk of widespread outages and improving reliability.
Which Windows database stores many OS and application configuration settings centrally
A Page file
B Boot loader
C Registry database
D Swap space
The Windows Registry stores configuration data for hardware, system settings, and applications. Because it is central, incorrect edits can break software or boot, so it is managed carefully.
Which OS mechanism queues print jobs on disk so apps do not wait for slow printers
A Paging
B Swapping
C Mirroring
D Spooling
Spooling places print jobs into a queue and feeds them to the printer sequentially. Applications continue running while the OS manages the queue, improving responsiveness and shared printer handling.
Which mechanism temporarily stores data in memory during I/O to handle speed differences
A Aging
B Booting
C Buffering
D Patching
Buffering uses memory areas to hold data while it is being transferred between devices and processes. It smooths speed differences and reduces waiting time during reads and writes.
Which OS action would most directly help if a new driver causes repeated system crashes after installation
A Roll back driver
B Increase page size
C Defrag disk
D Change wallpaper
Rolling back restores the previous stable driver version. It is a quick way to undo faulty updates without reinstalling the OS, often resolving crashes and device malfunctions immediately.
In user accounts, what is the major security advantage of using a standard account for daily work
A Speeds CPU clock
B Increases disk size
C Limits damage scope
D Improves screen quality
Standard accounts have limited privileges, so malware or mistakes cannot easily change system-wide settings or protected files. Admin rights are used only when required, improving overall system security.
Which concept best explains how a distributed OS can keep services available even if one machine fails
A Icon sorting
B Screen snapping
C File renaming
D Replication and failover
Replication keeps copies of data or services on multiple machines. Failover switches to a working node when one fails, improving availability and reliability for users in distributed environments.