OS Reviewer.docx

**IT ELECTIVE OPERATING SYSTEMS** **PPT \#1** COMPONENTS OF A COMPUTER SYSTEM - **Hardware:** Basic computing resources (CPU, memory, I/O devices). - **Operating System (OS):** Controls and coordinates hardware usage. - **Application Programs:** Software that uses system resources to...

**IT ELECTIVE OPERATING SYSTEMS** **PPT \#1** COMPONENTS OF A COMPUTER SYSTEM - **Hardware:** Basic computing resources (CPU, memory, I/O devices). - **Operating System (OS):** Controls and coordinates hardware usage. - **Application Programs:** Software that uses system resources to solve user problems (e.g., word processors, games). - **Users:** Individuals, machines, or other computers interacting with the system. - **SMALL COMPONENTS** - Process Management - Main Memory Management - File Management - I/O System Management - Secondary Memory Management - Networking - Protection System - Command-Interpreter System OPERATING SYSTEM - A sophisticated program running on the CPU with a main function called during boot. - Acts as an interface between users and computer hardware. - Hides hardware complexity from users. - Manages the overall operation of the computer system including hardware, security, and interfaces for both system and applications. KERNEL - in charge of the overall operation of the computer system. - Remains in memory and controls overall system operations. - Known as the "nucleus" of the OS. STARTING THE OS - **Booting:** Starting up a computer by loading the kernel. - **Bootstrap Program:** Code in ROM *[(firmware)]* that loads the OS from storage. - **BIOS (Basic Input/Output System):** runs at startup to load the OS. FUNCTIONS OF AN OPERATING SYSTEM - **Manages and Interacts with Computer Hardware:** - Controls CPU and RAM - Provides an interface for storage devices - manages I/O devices - *device drivers* = software programs that allow the hardware device to be used by the OS and by application software - **Provides and Manages System Security:** - Implements user authentication, protects data and software - **Single-user OS** - minimal security and user has full authority - **Multi-user OS** - login and password capability - protection of user's data stored on the server's central hard disk drives - protection and security for software programs - **Provides System Interface:** - **System Interface/Shell**: the interface between the user and the computer - User interaction through Command Line Interface (CLI) such as LINUX, DOS, UNIX or Graphical User Interface (GUI). - **Provides Interfaces for Application Software:** - Designed for specific CPU types and allows software compatibility. - Application software is developed for an operating system. OPERATING SYSTEM OBJECTIVES - **Convenience:** Makes the computer more convenient to use. - **Efficiency:** Allows computer system resources to be used in an efficient manner. - **Ability to Evolve:** Permit effective development, testing, and introduction of new system functions without interfering with service. SYSTEM DESIGN GOALS - **User goals**: convenient to use, easy to learn, reliable, safe, and fast. - **System goals**: easy to design, implement, and maintain, flexible, reliable, error-free, and efficient. TYPES OF OPERATING SYSTEMS - **Single-User/Single Tasking OS:** one user works at the OS and perform one task at a time - E.g., MS-DOS. - **Single-User/Multi-Tasking OS:** Most common form of OS used by PC and laptop and performs many tasks at once. - E.g., Windows, macOS, Linux. - **Multi-User/Multi-Tasking OS:** Many users connect to one computer and has a unique session. - E.g., UNIX, Linux. - **Real-Time Operating Systems (RTOS):** very fast small OS that is built into a device and quickly respond to user input. - E.g., Real-time Linux. HISTORY OF OPERATING SYSTEMS - Began in the 1940s with hardware like **ENIAC**. - Programs were loaded into memory manually using **switches, punched cards, or paper tapes.** - **Multiprogramming** means sharing of resources between more than one processes. - **Time-sharing systems** developed in the 1970s wherein multiple users have terminals (not computers) connected to the main computer and execute tasks on the main computer. - **Distributed** **systems** are similar to networks as they no longer need to exchange information explicitly. TODAY\'S OPERATING SYSTEMS - Multiple processors - **Load balancing:** Dynamically allocating tasks to the various processors. - **Scaling:** Breaking tasks into several subtasks equal to the number of processors available. - **The Network (Internet):** single network-wide operating system **PPT \#2** OPERATING SYSTEM (OS) - An OS is a program that manages computer resources and provides a user interface between users and hardware. KEY SERVICES PROVIDED BY AN OS - **Process**: program in execution, and the OS manages processes by allocating CPU time, memory, and I/O devices. - - - **First-Come, First-Served (FCFS)** - **Shortest Job First (SJF)** - **Round Robin (RR)** - - **Memory Management**: Ensures each process has access to the memory it needs to execute. - - - - - **File Management**: Organizes and stores data on disks. - - **File System Structures** - **Hierarchical**: Example: UNIX file system (e.g., /home/user/Documents). - **Flat**: Example: MS-DOS file system, where all files are in the same directory. - **Access Control**: Restricts access based on user permissions. OPERATING SYSTEM ARCHITECTURES - **Monolithic**: entire operating system is contained in a single executable file - - - **Microkernel**: Moves as much from the kernel into user space, using message passing. - - - **Hybrid**: Combination of monolithic and microkernel architectures. - VIRTUAL MACHINES - Treat hardware and the OS kernel as a unified hardware interface. - Types of Virtual Machines: - - SYSTEM CALLS - Interface between user-level programs and the kernel. - Examples: open(), close(), read(), write(), fork(), exec(). - Types of System Calls: - - - - - PPT \#3 PROCESS MANAGEMENT RESPONSIBILITIES OF THE OPERATING SYSTEM - **Process Creation and Deletion**: The OS manages the lifecycle of processes from creation to termination. - **Process Suspension and Resumption**: The OS can suspend processes (e.g., for resource management) and resume them as needed. - **Mechanisms for Synchronization and Communication**: The OS provides tools for processes to synchronize actions and communicate with each other. - **Resource Allocation and Scheduling**: The OS allocates CPU and memory resources to processes and schedules their execution. MULTIPROGRAMMING - **Definition**: Multiprogramming (or multitasking) allows multiple processes to share CPU and other resources. - **Objective**: To maximize CPU utilization by running multiple programs simultaneously. DIFFERENCE BETWEEN PROGRAM AND PROCESS **Program** **Process** -------------------------------------------------------------------------- ---------------------------------------------------------------------------------- A program is a set of instructions designed to complete a specific task. A process is an instance of an executing program. A program is a passive entity residing in secondary memory. A process is an active entity created during execution, loaded into main memory. A program exists until it is deleted. A process has a limited lifespan and terminates after completion. A program is static. A process is dynamic. A program requires memory space for instructions only. A process requires CPU, memory, and I/O resources. A program has no control block. A process has a Process Control Block (PCB). A program consists of code and data. A process requires additional management information. A program does not change itself. Multiple processes can execute a single program, with varying data. PROCESS STATES - **Created/New**: The initial state after creation, awaiting admission to the ready state. - **Ready**: Loaded into memory, waiting for CPU allocation. - **Running**: Actively executing on the CPU. - **Waiting**: Awaiting resource availability or I/O operations. - **Terminated**: Process has completed execution or has been killed. PROCESS CONTROL BLOCK (PCB) - **Definition**: a data structure in the operating system kernel containing the information needed to manage a particular process and called as \"the manifestation of a process in an operating system\" - **Location**: must be kept in an area of memory protected from normal user access or at the beginning of the kernel stack of the process. - **Attributes of PCB**: - Current state of the process - Process ID (PID) - Pointers to parent and child processes - Process priority - Memory allocation pointers - Register save area - I/O information (devices allocated, opened files) CONTEXT SWITCHING - **Definition**: The act of reassigning a CPU from one task to another one. It occurs when the kernel transfers control of the CPU from an executing process to another that is ready to run. - **When Context Switching Occurs**: - When a process exits. - When a process uses its time slice. - When a process requires unavailable resources. - When a higher priority process is ready to run. RESOURCE ALLOCATION AND SCHEDULING CONCEPTS - **Resource Types**: - **Pre-emptible Resources**: Can take resources away, and give them back later (e.g., CPU). - **Non-Preemptible Resources**: Once given resource, cannot be reused until voluntarily given up (e.g., disk blocks). - **Deadlock** -- two or more processes wait indefinitely for resources held by each other. - **Starvation** -- one or more processes never gets a share of the resource. SCHEDULING - **Definition**: The method of determining which process runs next from the ready queue. It also refers to the way processes are assigned to run on the available CPUs. - **Scheduler -** module that moves jobs or processes from queue to queue. - **Types of Scheduling**: - **Preemptive**: Scheduler can interrupt a job and force a context switch - **Non-Preemptive**: Scheduler waits for the running job to explicitly (voluntarily) block/terminate. CPU SCHEDULING CRITERIA - **CPU Utilization**: Keep CPU busy. - **Throughput**: Number of processes completed per time unit. - **Turnaround Time**: Time from submission to completion. - **Waiting Time**: Time spent waiting in the ready queue. - **Response Time**: Time from submission until the first response. - **Fairness**: Equal CPU time for all processes. LEVELS OF SCHEDULING - **Short-term Scheduling**: Decides which of the ready processes will execute next (dispatcher). - **Medium-term Scheduling**: Swaps processes in and out of memory. - **Long-term Scheduling**: Determines which processes enter the ready queue.