Topic in Operating Systems
Operating system structure describes how kernel components are organised and how programs request kernel services through system calls and system programs. Expect questions that contrast monolithic, layered, microkernel, modular and hybrid designs, with the usual trade-off of performance against isolation and reliability. Know the categories of system calls (process control, file manipulation, device management, information maintenance, communication and protection) and the three ways parameters are passed to the kernel: registers, a memory block, or the stack. Harder items cover loadable kernel modules, message-passing overhead in microkernels such as Mach and L4, virtual machines and hypervisors, and what formal verification of seL4 does and does not guarantee.
Below are 30 practice questions from a pool of 210 OS Structures MCQs, one of 12 topics in Operating Systems. Each shows the correct answer with an explanation; when you are ready, take a timed quiz to test recall under exam conditions.
Each question below shows the correct answer with a full explanation. Use these to build conceptual understanding before attempting a timed quiz.
Q1. Which of the following is a type of system call?
Process control (e.g., fork, exec, exit) is one of the main categories of system calls. Others include file management, device management, and information maintenance.
Q2. In a layered OS structure, the innermost layer is:
In the layered approach to OS design, the bottom layer (layer 0) is the hardware, and the highest layer is the user interface.
Q3. Which of the following is an example of a command-line interpreter?
Bash (Bourne Again Shell) is a command-line interpreter commonly used in UNIX and Linux systems that allows users to interact with the OS via text commands.
Q4. System programs provide:
System programs (system utilities) provide a convenient environment for program development and execution, including file management, status information, and programming language support.
Q5. The OS component that provides a graphical way to interact with the computer is called:
GUI (Graphical User Interface) provides a graphical, window-based way for users to interact with the operating system using icons, menus, and pointing devices.
Q6. Which system call is used to create a new process in UNIX?
The fork() system call is used to create a new process in UNIX/Linux. It creates a child process that is a copy of the parent process.
Q7. A monolithic kernel is one where:
In a monolithic kernel, the entire operating system runs as a single program in kernel space. All OS services operate in kernel mode, which provides high performance but less modularity.
Q8. Which of the following manages how data is stored and retrieved on a disk?
The file system manages how data is stored, organized, and retrieved on storage devices such as hard disks and SSDs.
Q9. What is the role of device drivers in an OS?
Device drivers act as translators between the hardware devices and the operating system, providing a standard interface for the OS to communicate with diverse hardware.
Q10. Linux is an example of which type of kernel?
Linux uses a monolithic kernel architecture where all core OS services (file systems, device drivers, networking) run in kernel space as part of a single large program.
Q11. In a microkernel OS, which of the following typically runs in user space?
In a microkernel architecture, services like file systems, device drivers, and network protocols run in user space. Only essential services like IPC and basic scheduling remain in the kernel.
Q12. What is the primary mechanism microkernels use for communication between services?
Microkernels primarily use message passing through Inter-Process Communication (IPC) for communication between services running in user space, since they cannot make direct kernel function calls.
Q13. System calls are typically invoked by user programs through:
User programs typically invoke system calls through APIs (like POSIX API or Win32 API) rather than making direct system calls, providing portability and ease of use.
Q14. What is the main disadvantage of the layered approach to OS design?
The layered approach suffers from difficulty in appropriately defining layers and performance overhead because a request must traverse multiple layers, with each layer adding processing overhead.
Q15. What is a loadable kernel module (LKM)?
A loadable kernel module is code that can be dynamically loaded into or removed from the kernel at runtime, commonly used for device drivers without needing to reboot the system.
Q16. Which of the following is a category of system calls?
The main categories of system calls include: process control, file management, device management, information maintenance, and communications.
Q17. Parameters to system calls can be passed by placing them in:
Parameters to system calls can be passed via registers, pushed onto the stack, or stored in a block/table in memory with the address passed in a register. The method depends on the number of parameters.
Q18. The POSIX API is:
POSIX (Portable Operating System Interface) is an IEEE standard that defines a standard operating system interface and environment, ensuring portability across UNIX-like systems.
Q19. What is the purpose of the system call interface?
The system call interface serves as a link between API function calls made by user programs and the actual system call implementations in the kernel, often using a numbering scheme.
Q20. Windows NT uses which type of kernel architecture?
Windows NT uses a hybrid kernel architecture that combines aspects of both monolithic and microkernel designs, keeping some services in kernel space for performance while maintaining a modular structure.
Q21. In the Mach microkernel, what are the primary abstractions provided?
The Mach microkernel provides five primary abstractions: tasks (resource containers), threads (execution units), ports (communication channels), messages (data units), and memory objects (memory management).
Q22. What is an exokernel?
An exokernel provides minimal abstractions, allowing application-level management of hardware resources. It only ensures protection and multiplexing, giving library operating systems direct hardware control.
Q23. What is the purpose of a policy/mechanism separation in OS design?
Policy/mechanism separation means mechanisms should not dictate policies. Mechanisms determine how something is done, policies decide what will be done. This allows policies to change without modifying mechanisms.
Q24. What is the main concept behind a unikernel?
A unikernel is a specialized machine image constructed by compiling an application together with only the OS library components it needs into a single-address-space image, optimized for cloud/VM deployment.
Q25. In OS debugging, what is a core dump?
A core dump is a file containing the recorded state of the working memory of a process at a specific time, typically when the process has terminated abnormally, used for post-mortem debugging.
Q26. What is the strace command used for in Linux?
strace is a diagnostic and debugging tool in Linux that traces all system calls made by a process and the signals received by it, useful for understanding program behavior.
Q27. What is the advantage of the modular kernel approach over a pure layered approach?
The modular approach allows any module to call any other module, unlike the layered approach where communication must go through adjacent layers. This provides better flexibility and performance.
Q28. In system generation (SYSGEN), the OS is configured for a specific hardware platform. Which of the following is NOT typically determined during SYSGEN?
SYSGEN determines hardware configuration like CPU type, memory size, available devices, and OS options. User passwords are set during system administration, not during system generation.
Q29. What is the role of the Hardware Abstraction Layer (HAL) in Windows?
The HAL in Windows provides a consistent interface to the kernel and device drivers, hiding hardware-specific details. This enables the OS to be portable across different hardware platforms.
Q30. What distinguishes a library OS from a traditional OS design?
In a library OS design, OS services are provided as libraries linked directly into application programs, which may run on bare hardware or a thin hypervisor without a traditional kernel boundary.
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