Operating Systems Overview

Operating System Responsibilities

• The OS manages processes by: creating, deleting, suspending, resuming, and providing mechanisms for synchronizing and communicating between them.
• Allocating and scheduling resources for processes.

Multiprogramming and Multitasking

• Technique where multiple tasks (processes) share common processing resources, like the CPU.
• Aims to maximize CPU utilization by running multiple programs simultaneously.

Process vs. Program

• Program: A set of instructions executed by a computer.
• Process: An instance of a program in execution, active and consuming resources.

Distinction between Program and Process

• Program is static, residing in secondary memory.
• Process is dynamic, existing only during execution in main memory.
• Program is a passive entity, containing instructions.
• Process is an active entity, requiring resources for execution.
• Program has two components: code and data.
• Process has additional information for management and execution.

Process States

• Created (New): Process is first created and awaits admission to the "ready" state.
• Ready: Process is loaded into main memory and awaits execution.
• Running: Process is actively executing on the CPU.
• Waiting: Process is waiting for a resource (e.g., I/O) to be available.
• Terminated: Process has completed execution or been explicitly killed.

Process Control Block (PCB)

• Contains information about a process for management, including state, identification (process ID - PID), parent/child relationships, priority, memory locations, register values, and I/O information.

Location of the PCB

• The PCB is typically placed in a protected area of memory, often at the beginning of the process' kernel stack.

Context Switching

• Reassigning CPU from one task to another.
• Involves saving the context (CPU registers and data) of the current process and loading the context of the new process.
• Triggers when a process exits, exhausts its time slice, requires unavailable resources, or a higher-priority process becomes ready.

Resource Allocation Concepts

• Pre-emptible Resources: Can be taken away and given back later (e.g., CPU).
• Non-pre-emptible Resources: Once assigned, cannot be reused until voluntarily released (e.g., disk blocks).

Scheduling Concepts

• Scheduling: Determining which process in the ready queue will run next.
• Scheduler: Software responsible for assigning processes to CPUs.
• Preemptive Systems: The scheduler can interrupt a process and force a context switch.
• Non-preemptive Systems: The scheduler waits for the running process to voluntarily block or terminate.
• Scheduling Decisions: Occur when a process switches states (ready, running, waiting, terminated).

Scheduling Assumptions

• A pool of ready processes vying for the CPU.
• Processes compete for resources.
• The scheduler aims to allocate the CPU fairly and optimize performance criteria.

Process Behavior and CPU Scheduling

• CPU/IO Burst Cycle: Processes alternate between periods of CPU execution and I/O operations.
• IO-Bound Processes: Characterized by frequent I/O operations and short CPU bursts.
• CPU-Bound Processes: Perform extensive computation and have fewer, longer CPU bursts.

Criteria for CPU Scheduling

• CPU Utilization: Keeping the CPU busy as much as possible.
• Throughput: Number of processes completed per time unit.
• Turnaround Time: Time elapsed from submission to completion of a process.
• Waiting Time: Time spent in the ready queue.
• Response Time: Time from request submission to the first response.
• Fairness: Providing equal CPU time to each process.

This quiz covers the fundamental responsibilities of operating systems, including process management and resource allocation. It also distinguishes between programs and processes, along with the concepts of multiprogramming and multitasking. Test your understanding of these key concepts in operating systems.