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Interactive System Scheduling

In interactive systems, scheduling focuses on providing a responsive experience to users by quickly switching between tasks to avoid long wait times.

  • It aims to balance fairness, quick response times, and prioritization of important tasks.

Three commonly used scheduling algorithms in interactive systems are:

  • Round-Robin Scheduling
  • Priority Scheduling
  • Multiple Queues Scheduling.

Round-Robin (RR) scheduling is a preemptive scheduling algorithm where each process in the ready queue is assigned a fixed time slice, called a “quantum.”

  • Each process runs for a maximum of one quantum, and if it doesn’t complete, it’s placed back at the end of the queue. The CPU then moves to the next process in the queue. This cycle continues until all processes are completed.

Characteristics:

  • Preemptive: A process can be interrupted after its time quantum expires.
  • Fair: Each process gets an equal time slice in a cyclic order, ensuring no process is starved.
  • Suitable for time-sharing systems where fast response is essential.

Example:

Round-Robin Scheduling

In Priority Scheduling, each process is assigned a priority level, and the CPU selects the process with the highest priority for execution next. It can be either preemptive or non-preemptive:

  • In preemptive priority scheduling, if a new process arrives with a higher priority than the current process, the CPU preempts the running process.
  • In non-preemptive priority scheduling, the CPU finishes the current process before switching to the higher-priority process.

Characteristics:

  • Can be implemented as either preemptive or non-preemptive.
  • Priorities can be static (assigned when processes are created) or dynamic (adjusted during runtime based on specific criteria).
  • Often used in systems where certain tasks must run as soon as possible (e.g., real-time systems).

Example:

Priority Scheduling

In Multilevel Queue Scheduling, processes are divided into different queues based on characteristics like priority or process type (e.g., system processes, interactive processes, batch processes). Each queue may use its own scheduling algorithm, and the queues themselves have a priority hierarchy.

  • For example, high-priority queues might be scheduled with Round-Robin for system process and medium-priority might be scheduled with Shortest Job First for interactive process, while lower-priority queues use FCFS for batch jobs.

Characteristics:

  • Each queue operates independently with its own scheduling algorithm.
  • Queues are assigned different priority levels, and jobs in higher-priority queues are executed before those in lower-priority queues.
  • Useful in systems that handle different types of jobs, such as interactive, batch, and real-time tasks.

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