Question 1

What is the key difference between a process and a thread?

Accepted Answer

A process has its own memory space; threads within a process share the same memory space. Each process has isolated memory (heap, stack, code). Threads within a process share heap and code but have their own stack. Threads are lighter to create and communicate faster, but share memory risks are higher.

Question 2

What is context switching in an OS?

Accepted Answer

Saving the state of a running process and restoring the state of another so the CPU can switch between them. During context switching, the OS saves the current process's CPU registers, program counter, and memory maps, then loads the next process's state. It enables multitasking but has overhead.

Question 3

What is the difference between preemptive and non-preemptive scheduling?

Accepted Answer

In preemptive scheduling, the OS can interrupt a running process; in non-preemptive, the process runs until it voluntarily yields. Preemptive (e.g., Round Robin): OS forcibly switches processes after a time quantum. Non-preemptive (e.g., FCFS): process runs until it blocks or finishes. Modern OSes are preemptive for better responsiveness.

Question 4

What is a semaphore in operating systems?

Accepted Answer

A synchronization primitive used to control concurrent access to a shared resource. A semaphore is a counter. wait() (P) decrements it; if it hits 0, the process blocks. signal() (V) increments it and wakes a waiting process. Binary semaphores (0 or 1) work like mutexes.

Question 5

What is a mutex?

Accepted Answer

A mutual exclusion lock allowing only one thread to access a shared resource at a time. A mutex (mutual exclusion) ensures only one thread can acquire the lock at a time. The thread that locks it must be the one to unlock it. Unlike a semaphore, it has ownership.

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