Operating Systems Previous Year Questions

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Corrected: the book's key says (c). A cycle in a resource-allocation graph does not always mean deadlock (with multiple instances), so A is false; B and C are correct.

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Semaphores are a synchronization tool. They control how concurrent processes access shared resources, which solves process synchronization problems, including mutual exclusion.

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Recursion uses a stack of activation records, scheduling uses a queue (first come, first served), and sorting can use a binary tree (as in a BST or heap).

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Stacks are used for parenthesis balancing and infix-to-postfix conversion, so (A) and (C) are correct. Process scheduling uses queues, not stacks.

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Swapping moves a whole process from main memory to disk (and back later) to free memory for other processes.

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Linux is a free, open-source operating system (kernel) released under the GNU GPL.

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Acquisition is the subconscious way a language is picked up through exposure and use. Learning is the conscious study of rules.

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A thread is called a lightweight process. Threads of the same process share its code, data and files, so creating and switching between them costs little.

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The diagram shows the ready queue, the I/O queues and the events that move a process between them. This is the queueing diagram of process scheduling.

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In paging, logical memory is divided into pages and physical memory into frames of the same size, so any page fits into any frame.

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Children with dyslexia struggle with reading text. Audio books and recorded material help them learn by listening while they follow the words.

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In ETL, the staging area is the intermediate storage where extracted data is cleaned and transformed before it is loaded into the data warehouse.

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Cache memory is a small, very fast memory between the CPU and main memory. It holds frequently used data and instructions, so programs run faster.

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A 14-unit job with a 2-unit quantum runs in 7 slices. A switch is counted between slices, giving 7 − 1 = 6 context switches.

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Aging gradually raises the priority of processes that have waited a long time. This prevents starvation (indefinite blocking) of low-priority jobs.

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UNIX inodes use an extended indexed scheme: 12 direct block pointers plus single, double and triple indirect blocks. This lets very large files be addressed.

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With FIFO and 3 frames: 7, 0, 1, 2 are faults (4 so far), 0 is a hit, then 3, 0, 4, 2, 3 are all faults. That gives 9 page faults.

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With a quantum of 4: P1 runs 0–4, P2 runs 4–7, P3 runs 7–10, then P1 runs 10–30. Waiting times are P1 = 6, P2 = 4, P3 = 7. The average is 17/3 ≈ 5.66 units.

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In SCAN, the disk arm moves to one end, then reverses, serving requests along the way, like an elevator. C-SCAN, not SCAN, gives more uniform waiting time.

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The banker's algorithm avoids deadlock (by checking for a safe state); it does not prevent it. Prevention means removing one of the four necessary conditions.

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Shortest Job First runs the shortest tasks first, so the average waiting time is minimised and the most jobs are completed per unit time.

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Demand paging loads a page into memory only when it is referenced, which triggers a page fault.

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The OS stores each process's state, program counter, registers, scheduling and memory information in its Process Control Block (PCB), which it uses to save and restore the process during context switches.

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In the buddy system, when a block is freed, it can be quickly merged with its free buddy to form a larger segment. This merging is called coalescing.

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Sorting is defined as re-arranging a given set of objects in a specific order (Wirth's definition). The other options describe why sorting is useful, not what sorting is.

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Demand paging (virtual memory) loads pages only when they are needed, so a program larger than physical memory can still run. Thrashing is a performance problem, not a technique.

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With n processes each needing k units, n(k−1) + 1 units guarantee no deadlock: 3 × (2−1) + 1 = 4.

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Java's garbage collector automatically reclaims the memory of objects that are no longer referenced by any part of the program.

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The OS keeps each process's state, program counter, registers, scheduling and memory information in its Process Control Block (PCB).

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Throughput is the number of processes completed per unit time. Turnaround time is the time to complete one process, and response time is the time to first response.

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Memory allocation and managing resources for efficient utilization are both core functions of an operating system.

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The four Coffman conditions are mutual exclusion (non-sharable resources), hold and wait, NO preemption and circular wait. Preemption itself prevents deadlock, so it is not a condition.

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Shortest Seek Time First is disk scheduling, Shortest Job First is CPU scheduling, Least Recently Used is page replacement, and the Banker's algorithm is deadlock avoidance.

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Semaphores can be implemented in software (e.g., with OS/kernel code or algorithms like Peterson's) and with hardware support such as test-and-set or atomic instructions.

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FIFO with 3 frames: faults on 3, 4, 2; 3 hits; then faults on 9 (out 3), 1 (out 4), 6 (out 2), 3 (out 9), 4 (out 1), 9 (out 6). Total = 9 faults.

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A process goes from running to waiting only when it waits for I/O or for an event. A lower-priority arrival never affects the running process (a higher-priority arrival may preempt it to ready).

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The Immediate window shows/evaluates current variable values, the Properties window shows the selected object's properties, Project Explorer lists forms and modules, and the Design window is where the form is designed.

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Pattern recognition first acquires data, then extracts features, then matches them against stored patterns, and finally classifies.

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CRM covers the methods, technology and capabilities a business uses to manage and analyse its interactions with customers.

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Simulation imitates how a real-world process or system behaves over time, using a model.

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Digitizing the coordinates is sampling, and digitizing the amplitude values is quantization.

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Debates and discussions on social issues, and teaching students to cooperate, both make social science learning participatory.

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The kernel is the core of the OS. It stays resident in main memory and manages the CPU, memory and devices. Other OS parts can be loaded only when needed.

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Reverse engineering analyses existing code to recover its design and requirements specification. It is often used when maintaining legacy software.

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Linux is a classic monolithic kernel. The Windows NT kernel also runs most OS services in kernel mode and is usually described as hybrid, but the exam treats both as monolithic.

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Threads give concurrency inside a single process. A process gives protection: each process has its own address space and resources. Both statements are true.

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A thread belongs to its process and shares only that process's resources, so it is private to the process. Threads of one process are not visible to other processes, so statement I is false.

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The standard process states are new, ready, running, waiting (blocked) and terminated. "Excite" is not a process state.

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C-SCAN is a disk scheduling algorithm. FCFS, SJF and SJN (shortest job next) are CPU scheduling algorithms.

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SRTF keeps choosing short jobs, so long jobs can starve. Round Robin gives every process a time slice quickly, so its response time is better than FCFS. Both statements are true.