Describe the difference between volatile and nonvolatile storage, including the impact each has on system performance and reliability.

Volatile memory , also known as dynamic or temporary memory, is a type of memory hardware that fetches and stores data at a very high speed. The operating system (OS) loads the volatile memory. The system stores its data and computer programs that the CPU may need in real-time within the volatile memory, and the data is automatically deleted as soon as the system shuts down. Advantages: fast, protects sensitive data (data not available after system turned off). Disadvantages: lower storage capacity, more expensive per unit. Examples: cache, RAM. Non-volatile memory , also known as static or permanent memory, is a type of memory hardware that does not lose the data stored in it when the system shuts down. Advantages: higher memory capacity, more cost-efficient. Disadvantages: takes longer to fetch data. Example: ROM.

· What is an Application Programming Interface (API)? Discuss its significance in the interaction between applications and the operating system.

An Application Programming Interface (API) is a set of predefined rules, protocols, and tools that allows software applications to communicate with each other. In the context of an operating system, an API provides a standardized way for applications to request services such as memory management, file access, input/output operations, and process control. APIs act as a middleman between the application and the operating system. Instead of directly interacting with the hardware or writing complex low-level code, developers use APIs to perform tasks like reading a file, printing a document, or allocating memory. This abstraction simplifies software development and ensures that applications are compatible with different versions of the operating system. APIs also enhance system stability and security by controlling how applications access system resources.

Explain the distinctions and relationships between a process and a thread, including an example of how each is used in operating systems.

A process is an independent program in execution that has its own allocated memory space, system resources, and execution context. It is managed by the operating system and represents a complete unit of work. A thread is a smaller unit of execution that runs within a process. A process can have one or multiple threads, all of which share the same memory space and system resources of that process. The key distinction between a process and a thread lies in resource management and isolation. Each process has its own memory area, threads share the memory of one process. Processes are completely isolated from each other, and threads can affect each other because they share the same memory area. Streams are easier to manage, they are created faster and easier. But since the threads share the same memory, a bug in one thread can break the entire process. Creating a process is more expensive, but the failure of one process does not affect the others. The relationship between threads and processes: hierarchical, a process is a container for threads. Example: process - running application (ex. Google Chrome), thread - page loading, handling user input, file downloading, etc.

· True or False? A program does not need to be stored in memory in its entirety before execution. Support your answer with a detailed explanation of how modern operating systems handle program execution.

True . A program does not need to be stored in memory in its entirety before execution. Modern operating systems use a technique called demand paging , which is part of the virtual memory management system. This allows programs to begin execution without loading the entire program into physical memory (RAM) all at once. When a program starts, the operating system loads only a small portion of the program into memory—typically the initial instructions and required data structures. The rest of the program stays on the storage device (such as a hard drive or SSD) until it's needed. As the program runs and tries to access parts of itself (code or data) that are not yet in memory, the hardware (usually the Memory Management Unit or MMU) raises a page fault . The operating system catches this page fault and then loads the required parts from disk into memory. This process is transparent to the user and the program, meaning the program continues to run as if all its parts were already in memory.

· What additional features do mobile operating systems often include beyond the core kernel? Explain how these features cater to mobile-specific functionalities.

Mobile operating systems include several additional features beyond the core kernel to support the unique needs of mobile devices like smartphones and tablets. Features: power management (to maximize battery life, Uses aggressive CPU throttling, sleep modes, and background process limits); Cellular and Network Stack Enhancements (to support mobile data (3G/4G/5G), Wi-Fi, Bluetooth, NFC, GPS. Includes hardware abstraction layers and APIs for managing these radios and switching between them smoothly); Touch and Gesture Interface (Allow intuitive interaction through fingers or stylus. Specialized input subsystems handle multi-touch, swipes, pinches); Push Notification Service (Enable apps to receive updates without running continuously. Uses cloud-based services (like Firebase Cloud Messaging or Apple Push Notification Service) that wake apps only when necessary).

· Explain the concept of a "system call" and discuss its importance in operating system architecture, including examples of common system calls.

A system call is a programmatic way for user-space applications to request services from the operating system’s kernel . Modern operating systems follow a privilege separation model : User Mode: Where regular applications run — limited access. Kernel Mode: Where the OS has full control over hardware and system resources. Since user programs can't directly interact with hardware (for security and stability), they use system calls to ask the kernel to act on their behalf . Examples: process control (fork(), exec(), exit()), file management (open(), read(), write(), close()), device management(ioctl(), write(), read()), information maintenance (getpid(), alarm(), sleep()).

· Describe the concept of CPU scheduling, its significance in operating system design, and how it affects system and application performance.

CPU scheduling is the process by which the operating system decides which process (or thread) gets to use the CPU at any given time. CPU Scheduling Significance: maximize CPU utilization, ensure fairness allocation of the resources, enhance responsiveness, reduces wait time. Common scheduling algorithms: First-Come First-Served, Shortest Job First, Round Robbin, Priority Scheduling, Multilevel Queue (Separate queues for types of processes). How CPU Scheduling Affects Performance System-Level Performance : Poor scheduling = idle CPU time or thrashing. Good scheduling = efficient multitasking and lower context switch overhead. Application Performance : Interactive apps rely on fast response times (low latency). Background tasks benefit from efficient throughput and fair scheduling. Real-Time Systems : Require predictable and guaranteed scheduling behavior (e.g., deadlines).

· What is a page fault? Explain the mechanism behind it and how operating systems handle page faults to manage memory efficiently.

A page fault occurs when a program tries to access a page in memory that is not currently loaded into the system's physical memory (RAM). This typically happens in systems that use virtual memory. Mechanism behind it: 1. A process tries to access a virtual address. 2. The Memory Management Unit (MMU) checks the page table . 3. If the page is not present in RAM: Page fault is triggered. 4. The OS must now load the missing page from disk into RAM. Steps to handle Page Fault: interrupt, access validation, find free frame (using algorithms: FIFO, LRU, CLOCK, OPTIMAL), load page from disk, update page table, resume process.

· List at least three resources that the operating system allocates and describe the strategies used for effective resource management.

1. CPU Time (Processor Time): The OS uses CPU scheduling algorithms to allocate processor time to different processes. Some common strategies include: First-Come First-Served, Round-Robin, Priority Scheduling. 2. Memory (RAM): The OS manages memory allocation through techniques like: paging, segmentation, virtual memory. 3. I/O Devices (Disk, Network, etc.): The OS manages access to I/O devices by scheduling requests and using techniques like: Firts-Come First-Served, Shortest Seek Time First, Disk Scheduling Algorithms.

· Identify at least two crucial activities the operating system performs in connection with disk management and explain their importance.

1. File System Management: The OS organizes and manages how data is stored and retrieved from the disk using a file system (e.g., FAT32, NTFS, ext4). This includes keeping track of file names, locations, sizes, and permissions. It also manages directories and metadata. This activity is essential because it allows users and applications to store and access data in a structured and secure way. 2. Disk Scheduling and Access Control: The OS controls how and when disk read/write operations occur. It uses disk scheduling algorithms (like FCFS, SSTF, or SCAN) to optimize the order of access requests, reducing seek time and improving performance. Additionally, it ensures that only authorized users and processes can access certain parts of the disk, protecting data from unauthorized use or corruption.

Explain the concept of inter-process communication and discuss why it is crucial for operating system functionality.

Inter-process communication - refers to the mechanisms that allow processes to exchange data and signals with each other. It is essential for multitasking operating systems where multiple processes need to share information. Why is IPC important: allows multiple processes to access shared data, helps coordinate actions, avoiding conflicts like race conditions, enables division of tasks among multiple processes. Types of IPS Mechanisms: Pipes (Unidirectional data stream between processes), Named pipes – FIFOs (Like pipes but with a name, allowing unrelated processes to use them), Message Queues(Send and receive structured messages – queue system for handling user requests in order), Shared Memory (Multiple processes access the same memory area – used for high speed data exchange), Semaphores (Synchronization tool to control access to shared resources – prevents race conditions when writing to the same file), Sockets (Allow communication over network or locally (TCP/UDP)).

What is thrashing? Describe this condition and explain what leads to its occurrence in a system.

Thrashing is a condition where the operating system spends most of its time swapping pages in and out of memory instead of executing actual processes. It happens when there is insufficient physical memory and too many processes compete for RAM, causing frequent page faults and excessive use of virtual memory. Trashing leads to performance drop - the system becomes extremely slow because it's busy constantly swapping pages instead of doing useful work, it increases response time and waste system resources.

Describe the goal of "Data Privacy" within the context of operating systems and detail measures for its protection.

The goal of data privacy in operating systems is to ensure that user data is protected from unauthorized access, tampering, or leakage. This involves: 1. access control (Limits who can access which files, devices, or system resources: user permissions, role-based access), 2. encryption (Protects data at rest (on disk) and in transit (during network communication): file system encryption, encrypted backups), 3. user authentication (Ensures that only authorized users can log into the system: passwords, biometric authentication, two-factor authentication), 4. isolation between processes (Prevents one process from accessing or interfering with another’s memory or resources – each process runs in its own protected memory space). Maintaining data privacy is critical for security and user trust.

What kernel data structure is commonly used for passing parameters to system calls? Explain its structure and function.

Kernel data structure – inner structure, used in operation system for management of processes, memory, files, etc. Examples: PID, Page Table, File Descriptor Table. When a user-space program needs to request a service from the operating system (like reading a file, allocating memory, or opening a socket), it performs a system call . Since user programs cannot directly access kernel code for safety, the request must go through a controlled interface — the system call interface . The system call interface uses a structure called a "register set" or "system call frame" , which contains parameters passed from user space to the kernel. Typically, parameters are passed using CPU registers (like in x86: EAX, EBX, ECX) or via a stack structure . This data is managed by the OS to correctly map user requests to kernel functions.

Reiterate the role of the process scheduler and discuss its impact on both system performance and user experience.

The process scheduler is a core component of the operating system kernel responsible for deciding which process or thread runs on the CPU at any given moment . Since CPUs can typically run only one process per core at a time, the scheduler must share CPU time among all runnable processes. Main goals of the scheduler: maximize CPU utilization, minimize response time, prevent any process from starving, support real-time constraints. Impact on system performance: good scheduling improves responsiveness, efficiency, CPU and resources utilization; poor scheduling can lead to starvation, high latency, unfair distribution of CPU time. Impact on user experience: faster response when switching windows, opening apps, smooth video and audio playback, stable performance while multitasking.

What must be done to a disk before it can be used for storage? Describe the process and explain why each step is necessary.

1. Partitioning - dividing the disk into one or more sections, called partitions . Needed to organize storage locally. 2. Formatting - writing a file system structure onto the partition. Needed to allow OS manage files and directories. 3. Mounting (for UNIX/Linux systems) - a ttaching the formatted partition to the system's directory tree. Needed for users and applications to access the disk in specific location.

What is virtual memory? Explain how it is implemented and why it is important in modern operating systems.

Virtual memory is a memory management technique that gives the illusion of a large, continuous memory space, even if the physical RAM is smaller. It allows processes to use more memory than physically available by using disk space as temporary memory . How it’s implemented: 1. Paging. Memory is divided into fixed-size blocks called pages (in RAM) and page frames (on disk). A page table maps virtual addresses (used by programs) to physical addresses (actual RAM locations). 2. Page Replacement. If RAM is full, some pages are moved to disk (called the swap space ) to make room for active pages. 3. Translation Lookaside Buffer (TLB). A special cache that speeds up address translation from virtual to physical. 4. Demand Paging. Pages are only loaded into RAM when they are actually needed, saving memory. Why it’s important: for multitasking (allows multiple applications to run simultaneously), for process isolation (every process has its own memory space), for efficiency (not all parts of a program need to be in RAM at once — saves resources).

Define context switching. Describe its impact on system performance and how operating systems minimize its overhead.

Context switching is the process of saving the state of a currently running process or thread and restoring the state of another process or thread so that execution can continue from where it left off. Impact on system performance: overhead (context switching uses CPU time but doesn’t perform useful work during the switch itself), cache effects (The new process may not benefit from cached data used by the previous one), frequent switching (increases this overhead and slows overall system performance). Ways to minimize overhead: efficient scheduling, time slicing (using optimal time slices to balance responsiveness and overhead), processor affinity (keeping a process on the same CPU core to reduce cache misses).

Explain demand paging and how it differs from pure paging.

Demand paging is a memory management technique where pages are only loaded into RAM when they are needed , not at the start of a program’s execution. If a page is not in memory when it’s accessed, a page fault occurs, and the OS loads it from disk. In pure paging (also known as pre-paging ), all the required pages of a process are loaded into RAM upfront , even if they’re not used immediately. Difference: Demand Paging = load on access → more efficient memory use, slower at first access. Pure Paging = load all at once → faster initial access but may waste memory on unused pages.

What is the difference between internal and external fragmentation in memory management?

Internal fragmentation occurs when allocated memory blocks have unused space inside them. For example, if a process needs 6 KB and is given an 8 KB block, 2 KB is wasted inside the block. External fragmentation occurs when there is enough total free memory , but it is scattered in small non-contiguous chunks, so larger allocations can’t be satisfied. Difference: Internal = wasted inside allocated blocks. External = wasted between allocated blocks (scattered free space).

· Describe the steps involved in the booting process of an operating system.

The boot process is a sequence of steps that are performed when you turn on your computer or other digital device to prepare it for operation. Steps: 1. Power On. 2. POST (Power-On Self Test) - hardware check. 3. Loading BIOS/UEFI. BIOS - built-on SW, that manages base settings. 4. Bootloader finds and loads OS kernel. Example, Windows Boot Manager. 5. Loading the system kernel. 6. OS running services and system processes (graphics, sound, network). 7. Appearing of the UI. Example (on Windows): Turned on the computer → BIOS checks the memory → finds the hard drive → starts the bootloader → Windows boots → the login screen appears.

· What is the difference between monolithic and microkernel architecture? Provide one advantage of each.

Monolithic versus microkernel: A monolithic kernel places most operating‑system services—file systems, drivers, networking and scheduler—inside one privileged address space, giving high performance because subsystem calls are simple function calls. A microkernel keeps only minimal primitives such as inter‑process communication, scheduling and low‑level memory management in kernel mode while drivers and servers run in user space, improving reliability because a faulty driver can be restarted without crashing the whole system.

· Explain the purpose of device drivers and how the OS uses them to interact with hardware.

Device drivers are specialized software that allow the operating system to communicate with hardware devices. Each driver acts as a translator between the OS and a specific piece of hardware, such as a printer, keyboard, or graphics card. When an application or the OS needs to use a device, it sends high-level commands to the driver, which then converts them into low-level instructions that the hardware can understand. This abstraction lets the OS work with different hardware types without needing to know the technical details of each one.

· Explain the role of DMA (Direct Memory Access) in improving system performance.

DMA (Direct Memory Access) improves system performance by allowing certain hardware devices to transfer data directly to and from the main memory without involving the CPU. This frees the CPU from handling every byte of data, reducing its workload and allowing it to perform other tasks simultaneously. As a result, data transfers become faster and more efficient, especially for high-speed devices like disk drives or graphics cards.

· What is a semaphore? Describe how it is used to manage process synchronization.

A semaphore is a synchronization tool used to control access to shared resources in a concurrent system. It is a variable that is used to signal whether a resource is available. Semaphores help prevent race conditions by allowing only a certain number of processes to access a critical section at the same time. There are two main types: binary semaphores (which allow one process at a time) and counting semaphores (which allow a limited number). Processes use "wait" (or "P") to decrease the semaphore and block if it's zero, and "signal" (or "V") to increase it and wake waiting processes.

· Define time-sharing systems and discuss how they differ from batch processing systems.

Time-sharing systems allow multiple users to access a computer system simultaneously by rapidly switching between them, giving the illusion that each user has their own dedicated machine. The CPU allocates short time slices to each user process in a round-robin or priority-based manner. In contrast, batch processing systems execute jobs in batches without user interaction, processing them one after another. While batch systems are efficient for long, repetitive tasks, time-sharing systems are designed for interactive use, providing faster response times and better user experience.

· What is memory swapping, and in what situations is it used?

Swapping transfers an entire process image from RAM to a swap area on disk to free memory and reloads it when the process is scheduled again. It is used during severe memory pressure or hibernation to release large blocks of RAM, but because the transfer is slow modern systems prefer page‑level paging and resort to full swapping only as a last measure.

· Compare preemptive and non-preemptive scheduling. Give one advantage and one disadvantage of each.

Pre‑emptive versus non‑pre‑emptive scheduling: In pre‑emptive scheduling the kernel can interrupt a running task after its time slice or when a higher priority task becomes ready. The advantage is good responsiveness and fairness; the disadvantage is extra context‑switch overhead and greater complexity in concurrent programming. In non‑pre‑emptive scheduling a task uses the CPU resources until it releases or blocks. The advantage is simpler implementation and fewer context switches; the disadvantage is that a runaway task can monopolize the processor and stall other work.

· What is a race condition? Describe one technique used by operating systems to prevent it.

A race condition occurs when two or more threads access shared data and the final result depends on the order of their operations. For example two threads incrementing the same counter without synchronization may lose an update. Operating systems prevent races with synchronization primitives such as mutexes, semaphores, spinlocks and atomic compare‑and‑swap instructions that ensure only one thread enters a critical section at a time.

· Describe the concept of spooling and how it benefits system operations, particularly in printer management.

Spooling is a process where output data is temporarily stored in a disk-based queue, allowing slower devices like printers to process the data at their own speed. In printer management, the operating system saves each print job in a spool directory and quickly returns control to the application, so users don't have to wait. The system then sends the data to the printer as it becomes ready. This enables multiple users to submit print jobs at the same time, supports reordering or canceling tasks, and keeps the printer working efficiently without idle time.

OS tickets Flashcards

1.

FLASHCARD QUESTION

Front

Explain the concept of threads within traditional, heavyweight processes and the impact on resource management.

Back

Threads are lightweight units of execution within a traditional, heavyweight process. While traditional processes (also called heavyweight) have their own memory space and resources, threads within the same process share the same address space, open files, and global data but have separate stacks and registers. This shared environment allows for efficient communication and faster context switching compared to full processes, reducing the overhead of resource management. As a result, threads improve responsiveness and scalability in applications, especially on multicore systems, by allowing multiple tasks to run concurrently within a single process.

2.

FLASHCARD QUESTION

Front

Discuss the fundamental reason RAID is used in storage solutions, including how it enhances data reliability and performance.

Back

RAID (Redundant Array of Independent Disks) is used in storage solutions to improve both data reliability and performance by combining multiple physical disks into one logical unit. The fundamental reason for using RAID is to provide fault tolerance—if one disk fails, data is not lost thanks to redundancy techniques such as mirroring or parity. Additionally, RAID can boost performance by distributing read/write operations across multiple disks, allowing parallel access. Different RAID levels (e.g., RAID 0, 1, 5, 10) offer varying trade-offs between speed, redundancy, and storage efficiency depending on system needs.

3.

FLASHCARD QUESTION

Front

· What is the common name used to refer to the operating system program and why is it referred to as such?

Back

The common name used to refer to the operating system program is the kernel. It is called the kernel because it is the core component of the operating system that has full control over the system's hardware and manages crucial tasks like memory, processes, and device communication. Just like the kernel of a seed is at its center, the OS kernel is at the center of all system operations, acting as a bridge between hardware and software.

4.

FLASHCARD QUESTION

Front

· List three different ways for structuring an operating system and discuss the advantages and disadvantages of each structure.

Back

Monolithic Structure: In a monolithic OS, all components (file system, process management, device drivers, etc.) run in kernel mode as one large program. Advantages: High performance due to minimal overhead and direct access to system resources. Disadvantages: Poor modularity, difficult to debug and maintain, and a bug in one component can crash the entire system. Examples: MS-DOS, early UNIX.

Layered Structure: This structure organizes the OS into layers, each built on top of the lower one, starting from hardware at the bottom to the user interface at the top. Advantages: Clear separation of concerns, easier to design and debug, each layer interacts only with the one below it. Disadvantages: Can be inefficient due to overhead between layers; changes in lower layers may require redesigning upper ones. Examples: THE system (by Dijkstra), early UNIX modifications.

Microkernel Structure: Only the most essential functions (e.g., inter-process communication and basic scheduling) reside in the kernel, while others like device drivers and file systems run in user space. Advantages: Improved reliability and security, as most services run independently in user mode; easier to modify and extend. Disadvantages: Lower performance due to more context switching and communication between kernel and services. Examples: MINIX, QNX, modern versions of macOS (based on XNU).

5.

FLASHCARD QUESTION

Front

· Provide at least two advantages of multiprocessor systems and explain how they contribute to enhanced computing performance.

Back

Multiprocessor systems offer several advantages, two of the most significant being increased throughput and enhanced reliability.
First, with multiple processors working in parallel, the system can execute more processes simultaneously, significantly improving overall throughput and reducing response time for users.
Second, reliability is improved because if one processor fails, the others can continue to operate, allowing the system to maintain partial functionality instead of crashing entirely.
Together, these benefits contribute to better scalability, faster processing, and greater fault tolerance, making multiprocessor systems ideal for high-performance computing environments.

6.

FLASHCARD QUESTION

Front

· Describe three strategies for selecting a free hole from the set of available holes in memory management and their impact on system efficiency.

Back

In memory management, when using dynamic partitioning, the system must select a suitable free hole (block of memory) to allocate to a process. Three common strategies are:

1. First-Fit: The system allocates the first hole that is large enough.
Impact: Fast and simple, but may lead to many small leftover holes at the beginning of memory (external fragmentation).

2. Best-Fit: The system searches for the smallest hole that is large enough.
Impact: Reduces wasted space, but tends to leave many very small unusable holes; slower than first-fit due to full search.

3. Worst-Fit: The system selects the largest available hole.
Impact: Leaves large leftover holes, hoping they are more useful later, but often leads to inefficient use of memory and fragmentation.

Each strategy impacts system efficiency differently in terms of fragmentation, search time, and memory utilization.

7.

FLASHCARD QUESTION

Front

· Define an interrupt and explain its essential role in handling system requests.

Back

An interrupt is a signal sent to the CPU by hardware or software to indicate that an event needs immediate attention. It temporarily halts the current execution so the processor can address the incoming request, such as I/O completion, a timer signal, or an error. Interrupts play a crucial role in efficient system operation by allowing the CPU to respond to asynchronous events without constantly checking device statuses (polling). This enables better multitasking, resource utilization, and responsiveness in modern operating systems.

8.

FLASHCARD QUESTION

Front

· Describe the two basic goal groups that must be considered when designing an operating system and how they influence design decisions.

Back

When designing an operating system, two basic goal groups must be considered: user goals and system goals.
User goals focus on making the system easy to use, reliable, secure, and responsive. These goals ensure that the OS provides a smooth and intuitive experience for end-users and developers.
System goals, on the other hand, emphasize efficiency, flexibility, and resource management. They aim to optimize performance, ensure fair resource allocation, and maintain system stability under various workloads.
Balancing these two goal groups is crucial: design decisions such as scheduling algorithms, memory management strategies, or user interface models must consider both usability and technical performance to build a well-functioning operating system.

9.

FLASHCARD QUESTION

Front

· What are the four components of a process? Explain each component's role in the process's lifecycle.

Back

A process consists of four main components: stack, heap, data section, and text section.

Stack: This contains temporary data such as function parameters, return addresses, and local variables. It grows and shrinks dynamically during function calls and returns. It plays a key role in controlling the process’s execution flow.
Heap: This is used for dynamic memory allocation at runtime (e.g., using malloc() in C). It grows as needed and stores data that is manually allocated and freed by the programmer.
Data section: This stores global and static variables that are initialized before execution begins. It remains allocated throughout the process's lifetime and holds values that persist across function calls.
Text section: This contains the actual executable code (machine instructions) of the program. It is usually marked as read-only to prevent accidental modification.

Together, these components define the structure and behavior of a process during its lifecycle, from creation and execution to termination.

10.

FLASHCARD QUESTION

Front

· True or False? Shared memory is typically not implemented using memory mapping. Justify your answer with reasoning.

Back

False.
Shared memory is typically implemented using memory mapping, especially in modern operating systems. Memory mapping allows multiple processes to map the same region of physical memory (or a file) into their virtual address space. This enables them to access the same data in memory efficiently, without the need for explicit message passing. Using memory mapping for shared memory improves performance and simplifies inter-process communication by allowing direct read/write access to shared regions.

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