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OS · Question Set
Process Management interview questions for placements and exams.
Questions
11
Included in this set
Subject
OS
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Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for OS.
Classic IPC mechanisms include shared memory, message queues, pipes, sockets and semaphores. Virtual memory is a memory management technique, not an inter‐process communication channel.
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A Process Control Block, or PCB, is a data structure used by the operating system to store all information about a process. It holds the process identifier (PID), process state (such as ready, running, waiting), CPU register values, memory limits, list of open files, scheduling information like priority or quantum, and pointers to parent and children processes. The OS uses the PCB when it needs to switch into or out of a process, resume the process later, or manage its resources.
Standard process states are Running (executing on CPU), Ready (waiting for CPU), and Waiting/Blocked (waiting for I/O or event). "Suspended" is used in some systems as an additional state when the process is swapped out, but it is not part of the classic simple lifecycle model.
In priority scheduling, if processes with low priority keep arriving, then a low priority process might never get CPU time. Without an aging mechanism (which increases priority over time), starvation becomes possible. FCFS and non-preemptive SJF will eventually serve everyone; Round Robin gives each process a time slice so starvation is less likely.
Multiprogramming allows multiple programs to be in memory at once. When one program is waiting for I/O, the CPU switches to another program so the CPU stays busy. This improves utilization of the CPU and overall throughput in a system with serial I/O operations.
In preemptive scheduling the operating system can interrupt a running process (for example when its time slice expires or a higher priority process arrives) and switch to another process. For instance, Round Robin and priority with preemption are preemptive algorithms. Non-preemptive scheduling means once a process starts running it will continue until it finishes or blocks for I/O; the OS does not forcibly take the CPU away. First-Come-First-Served (FCFS) and non-preemptive SJF are examples. Preemptive gives better responsiveness but adds overhead from context switches; non-preemptive is simpler but may lead to worse response times and poor handling of interactive tasks.
The dispatcher is the component of the operating system that gives control of the CPU to the process selected by the scheduler. It performs the context switch, switching from kernel mode to user mode, and jumps to the correct place in the user program to restart it. Its responsibilities include switching context, jumping to user code, and switching to user mode. The time the dispatcher takes (dispatch latency) affects how quickly a ready process begins execution, and therefore influences system responsiveness.
The ready queue is the data structure or list maintained by the operating system where all processes that are ready and waiting for CPU time reside. The scheduler picks one from this queue to run next. Other queues include waiting (blocked) queue for I/O, and termination queue for completed processes.
CPU scheduling aims to optimise several metrics so the system runs efficiently and fairly. These goals include maximising CPU utilization (keeping the CPU as busy as possible), maximising throughput (number of processes completed per unit time), minimising turnaround time (time from submission to completion), minimising waiting time (time a process waits in the ready queue), and minimising response time (time from request submission to first response) especially in interactive systems. An operating system must balance these often-competing goals when choosing its scheduling algorithm.
A context switch is the process of saving the state of the currently running process (such as register values, stack pointer, program counter) into its PCB and then loading the state of another process so it can run on the CPU. This lets the OS switch the CPU from one process to another. Minimising context switch time is important because each switch incurs overhead—saving and loading registers, updating memory maps, flushing translation lookaside buffers (TLB), and switching caches. High context‐switch overhead reduces CPU efficiency and can degrade overall system performance.
A process is an independent execution unit with its own address space and resources. A thread is a lightweight unit within a process that shares that address space and resources but has its own stack and program counter. This enables threads to communicate more easily and switch faster, but also means we must handle synchronization carefully when using threads.