Cpu Scheduling

Step 1: Definition of SJF.
SJF (Shortest Job First) is a non-preemptive CPU scheduling algorithm that selects the process with the shortest burst time for execution next. It minimizes the average waiting time.

Step 2: Analysis of other options.
- (1) FCFS: First Come First Serve executes processes in the order of their arrival, not based on burst time.
- (3) Round Robin: This algorithm assigns fixed time slices to processes, regardless of their burst time.
- (4) Priority Scheduling: Processes are scheduled based on their priority, not burst time.

Step 3: Conclusion.
The correct answer is **SJF**, which prefers the process with the shortest burst time.

Step 1: Explanation of Algorithms.
- **FCFS** (First Come First Serve): A non-preemptive scheduling algorithm that schedules processes based on their arrival order. If preemption is added, it becomes **FCFS + preemption** (I).
- **Round Robin**: A scheduling algorithm where processes are assigned a fixed time quantum and allowed to move between queues (II).
- **Multi-level queue scheduling**: This algorithm assigns processes to specific queues based on priority or other criteria, leading to often long average waiting time (III).
- **Multi-level Feedback Queue**: Processes can move between queues based on their behavior, and this algorithm does not permanently assign processes to one queue (IV).

Step 2: Match the list.
- (A) FCFS matches (I) FCFS + preemption. - (B) Round Robin matches (II) Allows the processes to move between queues. - (C) Multi-level queue scheduling matches (III) Often long average waiting time. - (D) Multi-level Feedback Queue matches (IV) Permanent assignment of processes to one specific queue.

Step 3: Conclusion.
Thus, the correct matching is **(A) - (I), (B) - (II), (C) - (III), (D) - (IV)**.

Step 1: Definition of CPU Scheduler.
The CPU scheduler, also known as the short-term scheduler, is responsible for selecting a process from the ready queue and allocating CPU time to it. This decision is made at a fast pace, typically every few milliseconds.

Step 2: Analysis of Options.
- (A) **Short Term Scheduler**: Correct, as it is the one responsible for the allocation of CPU time.
- (B) **Long Term Scheduler**: Incorrect, this scheduler determines which processes are admitted into the system, but does not directly schedule processes to the CPU.
- (C) **Medium Term Scheduler**: Incorrect, this scheduler manages the degree of multi-programming by swapping processes in and out of the memory.
- (D) **Asymmetric Scheduler**: Incorrect, this is not a standard term used for CPU scheduling.

Step 3: Conclusion.
The **Short Term Scheduler** is the CPU scheduler, so the correct answer is **(A) only**.

Step 1: Understanding the Concept:
CPU scheduling algorithms are classified as Preemptive or Non-preemptive. In preemptive scheduling, the OS can interrupt a running process to allocate the CPU to another. In non-preemptive scheduling, a process keeps the CPU until it terminates or switches to a waiting state.
Step 2: Detailed Explanation:
- Round Robin: Inherently preemptive as it uses time quantums.
- Shortest Remaining Time First (SRTF): This is the preemptive version of Shortest Job First (SJF).
- Priority Scheduling: Can be either preemptive or non-preemptive.
- First Come First Served (FCFS): This is a strictly non-preemptive algorithm. Once the CPU is allocated to a process, it cannot be taken back until the process completes its burst.
Step 3: Final Answer:
FCFS is always non-preemptive.