PlacementPrepWhich scheduling algorithm can cause starvation of long processes?
Solution
Short jobs keep arriving and are always picked first, so long jobs may wait indefinitely.
Answer: (A) Shortest Job First
Technical · CSE / IT
Operating Systems MCQs for placement tests
20 technical questions of moderate difficulty, as asked in campus placement and company tests. Each has a short explanation.
Round Robin scheduling uses a:
Solution
Each process runs for a fixed time slice, then goes to the back of the queue.
Answer: (D) Fixed time quantum
Which of these is NOT a necessary condition for deadlock?
Solution
The four conditions are mutual exclusion, hold and wait, no preemption, and circular wait.
Answer: (A) Preemption
The Banker's algorithm is used for:
Solution
It grants a request only if the system stays in a safe state.
Answer: (C) Deadlock avoidance
What is thrashing?
Solution
When too many page faults occur, the system spends most of its time paging.
Answer: (D) Spending more time swapping pages than executing
Which memory management scheme suffers from external fragmentation?
Solution
Paging uses fixed-size frames and avoids external fragmentation; variable-size allocation does not.
Answer: (B) Contiguous allocation (segmentation)
A page fault occurs when:
Solution
The page must be brought in from secondary storage.
Answer: (B) The requested page is not in main memory
Which page replacement algorithm can show Belady's anomaly?
Solution
With FIFO, more frames can sometimes cause more page faults.
Answer: (B) FIFO
A semaphore is used for:
Solution
Semaphores control access to shared resources.
Answer: (B) Process synchronisation
What is a process in an operating system?
Solution
A process is an active instance of a program.
Answer: (C) A program in execution
Threads of the same process share:
Solution
Each thread has its own stack, registers and program counter, but shares the process's memory.
Answer: (C) Code, data and open files
Which part of the OS stays in memory and provides core services?
Solution
The kernel manages processes, memory and devices.
Answer: (D) Kernel
Three processes with burst times 6, 3 and 8 arrive at time 0 in that order. What is the average waiting time under FCFS?
Solution
Waiting times: 0, 6 and 9. Average = 15/3 = 5.
Answer: (A) 5
Same processes (bursts 6, 3, 8, all at time 0). What is the average waiting time under non-preemptive SJF?
Solution
Order 3, 6, 8: waiting times 0, 3 and 9. Average = 12/3 = 4.
Answer: (C) 4
Which is the fastest form of memory in a computer?
Solution
Registers are inside the CPU and are faster than cache and RAM.
Answer: (A) CPU registers
Virtual memory allows:
Solution
Only the needed parts of a program are kept in RAM; the rest stays on disk.
Answer: (A) Programs larger than physical memory to run
A system call is:
Solution
System calls let user programs ask the kernel for services such as file I/O.
Answer: (D) A request from a program to the operating system kernel
Which scheduling is preemptive by design?
Solution
Round Robin interrupts a process when its time quantum ends.
Answer: (B) Round Robin
What is a race condition?
Solution
Without synchronisation, the result depends on which process runs first.
Answer: (D) Output depends on the timing of processes accessing shared data
A zombie process is a process that:
Solution
Its parent has not yet read its exit status.
Answer: (D) Has finished but whose entry remains in the process table
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