Priority Scheduling and Aging Concepts Quiz Quiz

Explore key priority scheduling and aging concepts in operating systems with this quiz designed to reinforce understanding of process management and scheduling strategies. This assessment covers foundational terms, potential issues like starvation, and the implementation of aging techniques to optimize CPU scheduling efficiency.

1. 1. Understanding Priority Scheduling

   In priority scheduling, how does the system decide which process will use the CPU next among several processes in the ready queue?

   1. Based on the lowest assigned priority number
   2. Randomly selected
   3. Based on first-come, first-served order
   4. Based on the highest assigned priority number

   Explanation: In priority scheduling, the process with the highest assigned priority number is chosen next to use the CPU. This is distinct from first-come, first-served scheduling, which simply picks the process that arrived first. Selecting based on the lowest number is incorrect, unless lower numbers indicate higher priority in a specific implementation, but generally, higher priority numbers take precedence. Processes are not chosen randomly in this method.

2. 2. Identifying a Scheduling Problem

   Which term describes the situation where low-priority processes are indefinitely delayed because higher-priority processes continuously arrive?

   1. Swapping
   2. Aging
   3. Starvation
   4. Priority inversion

   Explanation: Starvation occurs when low-priority processes do not get CPU time due to the continual arrival of higher-priority processes, causing potential indefinite postponement. Priority inversion is a different problem involving lower-priority processes holding resources needed by higher-priority ones. Aging refers to the technique used to prevent starvation, and swapping is a memory management operation, not related to CPU scheduling fairness directly.

3. 3. Purpose of Aging Technique

   What is the main goal of applying aging in priority scheduling algorithms?

   1. To gradually increase the priority of waiting processes
   2. To speed up all high-priority processes
   3. To ensure identical priorities for all processes
   4. To minimize the turnaround time for all tasks

   Explanation: Aging is used to prevent starvation by gradually increasing the priorities of processes waiting in the ready queue, ensuring that no process waits indefinitely. The main objective is not just to speed up high-priority processes or minimize turnaround time in general, but to balance fairness. Assigning identical priorities would defeat the purpose of priority scheduling and is not the aim of aging.

4. 4. Example of Priority Scheduling

   Given three processes with priorities 3, 7, and 5 (higher number means higher priority), which process will be scheduled first?

   1. The process with priority 3
   2. The process with priority 5
   3. The process that arrived first
   4. The process with priority 7

   Explanation: In this scenario, the process with priority 7 is the highest and will be scheduled first since the algorithm favors higher numbers. Processes with priorities 3 and 5 will wait unless 7 completes or is blocked. The arrival order only matters when priorities are equal, so 'the process that arrived first' is incorrect here.

5. 5. Preemptive vs Non-Preemptive Scheduling

   Which statement best describes preemptive priority scheduling?

   1. No process priorities are considered
   2. Once started, a process cannot be preempted by another
   3. A process always waits until it finishes, regardless of priority
   4. A running process can be interrupted if a higher-priority process arrives

   Explanation: Preemptive priority scheduling allows the operating system to interrupt the currently running process if a new process with higher priority comes in. In contrast, the second and third options describe non-preemptive scheduling. The final option ignores priority altogether, which is not characteristic of any priority-based system.

6. 6. Non-Preemptive Priority Scheduling

   In non-preemptive priority scheduling, what happens when a new process with higher priority enters the queue during the execution of a lower-priority process?

   1. The CPU immediately switches to the new process
   2. The running process continues until completion
   3. The higher-priority process is moved to the end of the queue
   4. Both processes are executed simultaneously

   Explanation: With non-preemptive scheduling, the current process is allowed to finish its CPU burst even if a higher-priority process arrives in the queue. Immediate switching only happens in preemptive scheduling. Simultaneous execution for both options is incorrect unless multiple CPUs are involved, which is not implied here. Moving the higher-priority process to the end of the queue also contradicts the premise of prioritization.

7. 7. Consequence of Not Using Aging

   What might occur in a priority scheduling system if aging is not implemented?

   1. The scheduling order becomes random
   2. Only higher-priority processes are delayed
   3. All processes finish at the same time
   4. Lower-priority processes may experience starvation

   Explanation: Without aging, low-priority processes might never get CPU time if higher-priority jobs keep arriving, leading to starvation. Finishing at the same time is generally impossible due to process differences. The third option misstates the problem, as higher-priority processes are rewarded in such systems. Random scheduling refers to an unrelated policy.

8. 8. Setting Process Priorities

   Which factor is commonly used to determine the initial priority of a process in operating systems?

   1. Type of application or user needs
   2. Network bandwidth usage
   3. Alphabetical order of processes
   4. The amount of free disk space

   Explanation: Process priorities are often initially set based on the type of application (such as real-time or background tasks) or specific user requirements. Disk space and network usage typically do not influence process priority assignment. The alphabetical order of process names is irrelevant to scheduling policies.

9. 9. Effect of Aging on Process Priority

   How does aging specifically help a process waiting in the queue for a long time?

   1. It decreases the process's priority
   2. It increases the number of processes in the queue
   3. It gradually boosts the process's priority
   4. It lowers the process's CPU burst time

   Explanation: Aging incrementally increases the priority of processes that have been waiting in the ready queue, thereby helping them eventually get scheduled. The option about lowering CPU burst time is unrelated to scheduling fairness. Decreasing a waiting process's priority would further worsen starvation. Increasing the number of processes in the queue is not an effect of aging.

10. 10. Priority Scheduling Drawback

    What is a significant drawback of simple priority scheduling without additional mechanisms like aging?

    1. CPU utilization becomes zero
    2. It always selects the oldest process first
    3. Starvation can occur for low-priority processes
    4. The CPU is shared equally by all processes

    Explanation: A major issue with basic priority scheduling is that it can lead to starvation for low-priority processes, as they may never get selected if higher-priority ones keep arriving. Equal CPU sharing is actually mitigated rather than enforced. Selecting the oldest process is a feature of other scheduling types, and zero CPU utilization is not a realistic outcome.