Uniprocessor scheduling refers to how an operating system (os) manages the execution of processes on single CPU. In uniprocessor system, only one process can run at a time, so the operating system needs to decide which process gets the CPU first and for how long. This decision is crucial for efficient functioning of a system.
When a computer is running multiple programs or processes, the CPU must allocate its time to different processes so that they can all make progress. However, because the CPU can only execute one instruction at a time, scheduling determines the order and duration for which each process gets access to the CPU. Good scheduling ensures that processes run smoothly without causing delays, making the system feel responsive to the user.
First-Come, First-Served (FCFS): In FCFS, the process that arrives first gets executed first. It's like standing in line: the first person in line is served first. However, FCFS can be inefficient if a long process arrives first, as it forces shorter processes to wait.
Shortest Job Next (SJN): This scheduling method selects the process with the shortest execution time first. This helps reduce the average time that processes spend waiting. However, one downside is that it requires knowing how long each process will take, which isn't always possible.
Round Robin (RR): In Round Robin, each process gets a small, fixed amount of time to run, called a "time slice" or "quantum." After its time is up, the CPU moves to the next process in the queue. This method ensures fairness, as every process gets a chance to run. However, if the time slices are too short, it can lead to frequent switching between processes, slowing down the system.
Priority Scheduling: In priority scheduling, each process is assigned a priority level. The CPU executes processes with higher priority first. Lower-priority processes may have to wait longer, which can sometimes lead to issues like "starvation," where a low-priority process waits indefinitely.
Uniprocessor scheduling is essential for managing how the CPU allocates its time to different processes. By using various scheduling algorithms like FCFS, SJN, Round Robin, and Priority Scheduling, the operating system can ensure that the CPU works efficiently.
