CPUScheduling

What is a Context Switch?

A context switch is the process of saving the CPU state of a currently running task and loading the saved state of another task, so a single CPU core can appea…

What is CPU Scheduling?

CPU scheduling is the OS mechanism that decides which ready process or thread gets to run on the CPU next, aiming to balance throughput, fairness, and responsi…

Preemptive vs Non-Preemptive Scheduling

Preemptive scheduling lets the OS forcibly suspend a running process to give the CPU to another, while non-preemptive scheduling requires the running process t…

What is an Interrupt?

An interrupt is a signal to the CPU, generated by hardware or software, that forces the processor to pause its current instruction stream and immediately trans…

What Is Round Robin Scheduling?

Round robin scheduling is a preemptive CPU scheduling algorithm that gives every process a fixed time slice, called a quantum, in a cyclic order, so no single…

What is First-Come-First-Served (FCFS) Scheduling?

First-Come-First-Served (FCFS) is a non-preemptive CPU scheduling algorithm that runs processes strictly in the order they arrive in the ready queue, giving ea…

What is Shortest-Job-First (SJF) Scheduling?

Shortest-Job-First (SJF) is a scheduling algorithm that always dispatches the ready process with the smallest total CPU burst time next, which provably minimiz…

What is Shortest-Remaining-Time-First (SRTF) Scheduling?

Shortest-Remaining-Time-First (SRTF) is the preemptive version of Shortest-Job-First: whenever a new process arrives, the scheduler compares its burst time to…

What is Priority Scheduling?

Priority scheduling dispatches the ready process with the highest priority value next, rather than by arrival order or burst time, and can be implemented as ei…

What is Multilevel Queue Scheduling?

Multilevel queue scheduling partitions the ready queue into several separate queues by process type — such as system, interactive, and batch — each with its ow…

What is Multilevel Feedback Queue Scheduling?

Multilevel feedback queue (MLFQ) scheduling uses several ready queues ranked by priority, each with its own time quantum, and moves a process between queues ba…

What is Lottery Scheduling?

Lottery scheduling is a probabilistic CPU scheduling algorithm that gives each process a number of lottery tickets proportional to its desired share of the CPU…

What is the Completely Fair Scheduler (CFS)?

The Completely Fair Scheduler (CFS) is the default Linux process scheduler that tracks each runnable task’s virtual runtime and always picks the task with the…

What is Earliest Deadline First (EDF) Scheduling?

Earliest Deadline First (EDF) is a dynamic-priority, preemptive real-time scheduling algorithm that always runs whichever ready task has the closest absolute d…

Round Robin vs Priority Scheduling: What is the Difference?

Round Robin gives every ready process an equal, fixed-size time slice in strict rotation regardless of importance, prioritizing fairness and responsiveness, wh…

What is Busy Waiting and Why is it Costly?

Busy waiting is when a thread repeatedly checks a condition in a tight loop instead of yielding the CPU or being put to sleep, which wastes CPU cycles and star…

How Does Thread Scheduling Work?

Thread scheduling is the mechanism by which the OS (or a user-space runtime) decides which of the runnable threads gets CPU time next, typically driven by prio…

What is a Process Control Block (PCB)?

A Process Control Block (PCB) is the kernel data structure that stores everything the OS needs to know about a process — its state, register values, memory map…

What are the Different Process States in an OS?

A process moves through a small set of states — new, ready, running, waiting (blocked), and terminated — and the OS scheduler transitions it between them based…

What Causes Context Switch Overhead and How Is It Reduced?

Context switch overhead comes from the direct cost of saving and restoring CPU state plus the indirect cost of losing cache, TLB, and pipeline warmth, and it i…

CPU-Bound vs I/O-Bound Processes: What Is the Difference?

A CPU-bound process spends most of its time performing computation and rarely blocks, while an I/O-bound process spends most of its time waiting on disk, netwo…

What is Turnaround Time in CPU Scheduling?

Turnaround time is the total time a process spends in the system, measured as completion time minus arrival time, and it includes waiting in the ready queue, e…

Waiting Time vs Response Time in Scheduling

Waiting time is the total time a process spends sitting in the ready queue without running, while response time is the time from when a process arrives until i…

What is Throughput in Operating Systems?

Throughput in an operating system is the number of processes completed per unit of time, and it measures overall system productivity rather than how any single…