Q1Operating Systems (Departmental Elective)

In a modern multiprogramming OS, CPU execution time is the absolute most valuable physical resource. The OS cannot allow processes to randomly seize the CPU. It relies on a highly rigorous, mathematical Process Scheduling architecture to guarantee absolute maximum CPU utilization and system responsiveness.

The Three Scheduling Tiers

• 1. Long-Term Scheduler (Job Scheduler): Operates extremely slowly. It mathematically decides which processes in the massive hard drive spool are allowed to physically enter the RAM's Ready Queue. It strictly controls the "Degree of Multiprogramming" (the total number of processes in RAM).
• 2. Short-Term Scheduler (CPU Scheduler): The absolute fastest, most violent scheduler. It executes every few milliseconds. Its singular objective is to instantly select a process from the Ready Queue and inject it directly into the CPU.
• 3. Medium-Term Scheduler: Utilized specifically in Virtual Memory architectures. It aggressively handles "Swapping." If the RAM is completely exhausted, it violently rips a suspended process out of RAM and swaps it to the Hard Drive to free up physical memory.

Strict Mathematical Scheduling Criteria

Engineers cannot blindly guess if an algorithm (like FCFS or RR) is good. They use strict mathematical metrics:

• CPU Utilization: The mathematical percentage of time the CPU is actively executing code (Target: 100%).
• Throughput: The absolute number of complete processes finishing execution per unit of time (e.g., 10 processes/second).
• Turnaround Time: The massive mathematical sum of time from the exact millisecond a process is submitted to the exact millisecond it terminates ($Wait\_Time+Burst\_Time$).
• Waiting Time: The total time a process spends violently trapped in the Ready Queue, waiting for the CPU.
• Response Time: The time from submission until the first physical response is generated, critical for interactive UI systems.