Operating Systems Overview
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What is one of the primary advantages of using Direct Memory Access (DMA)?

  • It requires less memory for data storage.
  • It allows the processor to idle during memory operations.
  • It enables the operating system to execute other tasks concurrently. (correct)
  • It simplifies the management of dynamic memory.

    • What occurs during a context switch in an operating system?

  • The processor resets to run the next process.
  • All processes are terminated to free up resources.
  • The current process's execution state is saved and another is loaded. (correct)
  • The memory allocation for the current process is expanded.

    • What is a disadvantage of using the many-to-one multi-threading model?

  • It complicates the memory address space management.
  • It can lead to high levels of CPU usage.
  • It restricts fault tolerance between threads.
  • Threads cannot execute in parallel, limiting performance. (correct)

    • Which of the following is an advantage of dynamic memory partitioning over static memory partitioning?

    <p>It avoids internal fragmentation.</p> Signup and view all the answers

    What is a potential problem when a memory manager swaps out a waiting process?

    <p>It can lead to loss of data integrity in other processes.</p> Signup and view all the answers

    What is the primary motivation for introducing concurrency in operating systems?

    <p>To allow simultaneous resource usage</p> Signup and view all the answers

    Which factor determines the upper limit of a working set in operating systems?

    <p>Degree of multiprogramming</p> Signup and view all the answers

    Under what condition is busy waiting considered an acceptable synchronization method?

    <p>When synchronization between separate processors is needed</p> Signup and view all the answers

    Which of the following instructions can be employed to implement binary semaphores?

    <p>Fetch&amp;Add</p> Signup and view all the answers

    In which scenario does the statement 'x:= y' not qualify as atomic?

    <p>When y is a shared variable</p> Signup and view all the answers

    What is a blocking factor in a file system?

    <p>The ratio of logical to physical blocks</p> Signup and view all the answers

    Which correctness concern in concurrent programming focuses on ensuring that all threads progress as expected?

    <p>Fairness</p> Signup and view all the answers

    What is the return path from kernel used for?

    <p>To execute checks after a system call or interrupt</p> Signup and view all the answers

    What is a key disadvantage of a spinlock in a single processor environment?

    <p>It can lead to inefficient resource use due to busy waiting.</p> Signup and view all the answers

    Which of the following components is NOT part of the steps in processing a system call?

    <p>Directly allocating new memory</p> Signup and view all the answers

    In the context of priority inversion, which situation best describes this condition?

    <p>A high-priority thread is blocked by a medium-priority thread due to resource sharing.</p> Signup and view all the answers

    What does system availability signify?

    <p>The likelihood that a system is operating as intended.</p> Signup and view all the answers

    Which approach is NOT typically used to handle deadlock situations?

    <p>Mitigation</p> Signup and view all the answers

    What is an observed property resulting from scheduling policies called?

    <p>Scheduling metric</p> Signup and view all the answers

    How can inspecting the value of a semaphore be beneficial in a program?

    <p>It helps prevent the blocking of a process by checking the semaphore value.</p> Signup and view all the answers

    What is meant by the interference of concurrent programs?

    <p>The incorrect behavior arising from local assumptions about a program's state.</p> Signup and view all the answers

    What is the main disadvantage of using a specific value in scheduling frameworks?

    <p>It may lead to the incorrect assertion of value being zero.</p> Signup and view all the answers

    Which of the following best describes inter-process communication through message passing?

    <p>It uses communication channels such as pipes and sockets.</p> Signup and view all the answers

    Which method is NOT a way to solve internal fragmentation caused by small files in file systems?

    <p>Increase the block size uniformly for all files.</p> Signup and view all the answers

    What distinguishes a process address space from the main memory address space?

    <p>Process address space provides a virtual view while main memory is physical.</p> Signup and view all the answers

    How does a CPU handle an interrupt?

    <p>It saves the current state, executes the ISR, and restores the state.</p> Signup and view all the answers

    What problem does internal fragmentation in file systems primarily cause?

    <p>Inefficient storage usage due to wasted space in fixed blocks.</p> Signup and view all the answers

    Which of the following describes the priority function in CPU scheduling?

    <p>It determines which process has the highest priority to execute next.</p> Signup and view all the answers

    Which is an optimization technique for storing small files within a file system?

    <p>Utilizing inode structures with direct and indirect blocks for space efficiency.</p> Signup and view all the answers

    What is the primary task of the top half of an interrupt handler?

    <p>Prepare for another interrupt by re-enabling it.</p> Signup and view all the answers

    Which RAID level primarily increases performance by distributing one logical disk over multiple physical disks?

    <p>RAID 0</p> Signup and view all the answers

    Which rule should be followed to avoid deadlock in action synchronization?

    <p>Avoid cycles in semaphore calls.</p> Signup and view all the answers

    What does the term 'interference' among concurrent processes imply?

    <p>Knowledge or assumptions of one process are disturbed by another.</p> Signup and view all the answers

    Under what condition is an assignment in Pascal or C regarded as atomic?

    <p>When there is at most one reference to a shared variable.</p> Signup and view all the answers

    Which of the following statements reflects the underlying assumption for atomic assignments?

    <p>Interrupts and hardware states are managed correctly during execution.</p> Signup and view all the answers

    What is a key goal of RAID levels 5 and 6 in terms of data management?

    <p>To distribute parity and avoid performance hot-spots.</p> Signup and view all the answers

    What does the concept of 'fairness' refer to in concurrent processing?

    <p>No process should be left waiting indefinitely for resources.</p> Signup and view all the answers

    What is the role of a device driver in an operating system?

    <p>To facilitate communication between the operating system and hardware devices.</p> Signup and view all the answers

    Which section of a critical region checks if a process can enter?

    <p>Entry section</p> Signup and view all the answers

    What happens during the action of a process transitioning from Running to Waiting?

    <p>It performs an I/O request or waits for an event.</p> Signup and view all the answers

    What is the core function of the operating system kernel?

    <p>To manage hardware resources and system calls.</p> Signup and view all the answers

    Why is running a web server as a single-threaded process discouraged?

    <p>It limits performance and leads to delays in handling requests.</p> Signup and view all the answers

    What is the consequence of thrashing in an operating system?

    <p>It results from excessive paging and degrades system performance.</p> Signup and view all the answers

    What is the effect of the kernel mode in an operating system?

    <p>It enables unrestricted access to all system resources.</p> Signup and view all the answers

    What is an advantage of using a thread pool in an operating system?

    <p>It reduces the overhead of repeatedly creating and destroying threads.</p> Signup and view all the answers

    Study Notes

    Operating Systems - General Notes

    • Operating systems act as intermediaries between users and hardware resources.
    • They manage and control computer hardware and software.

    Motivations for Operating Systems

    • Abstraction: Hides complex hardware details from users and applications.
    • Concurrency: Allows multiple tasks to run seemingly simultaneously.
    • Portability: Enables programs to run on different hardware with less modification.
    • Resource Management: Efficiently allocates and manages hardware resources (CPU, memory, I/O).

    Multi-threaded Programming

    • Motivation: Improves performance on multi-core processors and handles natural concurrency.
    • Working Set: The set of physical memory pages currently needed by a process. Lower and upper limits determine efficiency.
    • Synchronization: Controls access to shared resources by multiple threads and prevents race conditions.
    • Busy Waiting: Acceptable if synchronization time is minimal between processors, but not for multiprocessor synchronization.

    Correctness in Concurrent Programs

    • Functional Correctness: The program produces the expected results.
    • Minimal Waiting: Processes wait a reasonable amount of time.
    • Absence of Deadlocks: Avoids situations where two or more processes are permanently blocked.
    • Fairness: All processes get a fair share of resources and processing time.

    Return Path from Kernel

    • The sequence of actions the operating system performs to resume userspace execution after a system call or interrupt.

    Machine Instructions for Semaphores

    • Fetch&Add, Test&Set, Compare&Swap: Instructions used in implementing semaphores.

    Shared Variables in Statements

    • Single reference to a shared variable → atomic
    • Multiple references to shared variables → not atomic

    Principles for Condition Synchronization

    • Verify conditions (check for a true condition)
    • Notify other processes that a condition become true

    Multiple Threads vs. Multiple Processes

    • Multiple Threads: Easier to share data and resources between threads because they exist within the same memory space.
    • Multiple Processes: Each process has its own memory space and resources, reducing interference and improving stability.

    Kernel Control Methods

    • Interrupt: A signal from hardware requesting the kernel to take certain actions.
    • Trap: An instruction to transfer control from the user program to the kernel by the processor.
    • Execution: The kernel initiates actions, such as loading system calls

    Communication Methods

    • Mailbox communication: A communication queue used by multiple sender and receiver processes to communicate and pass data.

    Input/Output (I/O) Devices

    • Terminals: Used for user input/output. Examples: Keyboards and Monitors
    • Block Devices: Sequential-access storage. Examples: hard drives and floppy drives.
    • Communication Devices: Transport signals. Examples: Network interfaces and modems

    Critical Sections

    • Sections in a program that require mutually exclusive access to shared resources by threads and processes.

    Memory Management

    • Internal Fragmentation: Wastes space inside allocated blocks; occurs when allocated memory is larger than required.
    • External Fragmentation: Wasting space in memory due to non-contiguous blocks allocated and deallocated over time, making it harder for larger processes to fit.

    Deadlocks

    • Deadlocked Set: All tasks in the set are blocked or terminated. Any task that could unblock a non-terminated task is also in the set.
    • Deadlock Recovery: The actions taken by the operating system when a deadlock is detected.
    • Pre-emption: Temporarily taking away resources from processes.

    Scheduling

    • Scheduling: The process of assigning resources (e.g., CPU, memory) to tasks to maximize performance or meet specific requirements.
    • Metric: A specific metric used to assess scheduling performance.

    Spinlocks

    • Advantage: Fast and effective for single-core systems.
    • Disadvantage: Inefficient for multi-core systems due to busy-waiting behavior

    Priority Inversion

    • A situation where a low-priority process blocks a high-priority process, causing lower response times or system performance

    Memory Access Methods

    • Mode switching: Changing the execution context from user-level operations to kernel-level operations
    • Context switch: Saving and reloading the current process's state, to transition between multiple processes

    I/O Buffering

    • Advantages: Reduces CPU overhead (efficient utilization) and improves throughput by resolving speed conflicts between processors and devices.

    Local Variables

    • Variables are accessible by only one thread

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    Operating Systems Exam Notes Part 1 PDF

    Description

    This quiz covers fundamental concepts of operating systems, including their role as intermediaries between users and hardware resources. It discusses motivations for operating systems such as abstraction, concurrency, and resource management, along with multi-threaded programming principles.

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