OS tickets

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.

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.

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.

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).

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.

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.

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.

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.

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.

1. 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.

2. 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.

3. 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.

4. 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.

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.