1. Overall Process‐State Diagram (2 marks)

Long-Term Scheduler (Admission Scheduler) (3 marks)

• Role: Selects jobs from the Job Queue (on disk) and loads them into memory’s Ready Queue.
• Goal: Control the degree of multiprogramming (number of processes in memory).
• Frequency: Invoked relatively infrequently—only when the ready‐queue is low or system load changes.
• Effect:
  • Too many processes ⇒ thrashing, overhead.
  • Too few ⇒ CPU under-utilized.

Short-Term Scheduler (CPU Scheduler) (3 marks)

• Role: Chooses which ready process in memory gets the CPU next.
• Goal: Optimize CPU utilization and response time via a policy (e.g., Round-Robin, SJF, Priority).
• Frequency: Invoked on every:
  • Process switch (voluntary or time-slice expiry)
  • I/O completion (moving a process to ready queue)
• Boundaries:
  • Must be very fast (hardware timer + OS routine).
  • Works closely with the dispatcher, which performs the actual context switch.

Medium-Term Scheduler (Swapper) (2 marks)

• Role: Temporarily swaps entire processes out of memory to disk (→ Ready-Suspended or Blocked-Suspended queues) and later swaps in.
• Goal:
  • Improve memory utilization and reduce external fragmentation.
  • Regulate multiprogramming dynamically under memory pressure.
• Frequency: Moderate—triggered when:
  • Memory becomes scarce
  • Processes block for long I/O