CS2005 Networks and Operating Systems - Operating Systems Structures and Processes

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Course Title

• CS2005 Networks and Operating Systems

• Authors: A. Silberschatz, P. Baer Galvin, G. Gagne

• ©2003

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Course Overview

• Welcome to the OS part of CS2005

• Semester: 2

• Week 18: Operating Systems Structures and Processes (HTTP)

• Week 19: Threads (HTTP)

• Week 20: Process Synchronization (Concurrency)

• Week 21: Security (Concurrency)

• Week 22: No Lecture (Exam Brief, TCP/UDP)

• Week 23: Effective Learning Week

• Weeks 24-25: No Lectures

• Week 28: Revision Lecture (No Lectures/Labs, TCP/UDP, ICMP)

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Session Objectives

• Describe the services an operating system provides to users, processes, and other systems.

• Understand:

  • The meaning of a Process in an operating systems context.

  • The composition of a process and its scheduling in an operating system.

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Key Questions OS Structures

• What are the key services of an operating system?

• What are the main approaches to access operating system services?

• What are system calls and system programs?

Processes

• What is a Process?

• How does a Process get composed?

• What are the possible states of a Process?

• How is a Process scheduled in an operating system?

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Variety of Operating Systems

• Resource links for operating systems:

  • Wikipedia List of Operating Systems

  • Operating System Resource

  • Examples: ios, TinyOS, TIZEN

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Multimedia Resources

• Videos:

  • Linux backgrounder

  • TED Talk Linux

  • Unix at the Beginning

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OS Structures

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Operating System Services

• Provides an environment for program execution.

• Offers services that differ among operating systems but have common classes.

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Key Operating System Services

• User Interface (UI):

  • CLI (Command Line Interface), Batch Interface, GUI (Graphical User Interface).

• Program Execution:

  • Load and run programs, normal or abnormal termination.

• I/O Operations:

  • Indirect control of I/O devices.

• File-system Manipulation:

  • Manage reading, writing, creating, deleting files/directories, and manage permissions.

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More Operating System Services

• Communications:

  • Information exchange between processes, possibly on different systems.

• Implementations: shared memory, message passing.

• Error Detection:

  • Continuous monitoring for hardware and software errors; may lead to system halting or process termination.

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Additional OS Services

• Resource Allocation:

  • Manage resource allocation among multiple users/jobs.

• Accounting:

  • Track resource usage by users.

• Protection and Security:

  • Control access to information and ensure system security from unauthorized access.

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User Interface: Command Interpreter

• CLI allows direct command entry, sometimes implemented in the kernel or via higher-level system programs.

• Fetches and executes commands, often with batch processing.

• Examples: Windows cmd.exe, Unix/Linux shells (Bourne shell, C shell, BASH).

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User Interface: Batch Files

• Batch files run collections of CLI commands for various tasks.

• Resources:

  • Windows Batch Scripting

  • Network diagnostics examples: How to Write a Batch Script.

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User Interface: Graphical User Interface (GUI)

• User-friendly interface utilizing desktop metaphors; often includes mouse and keyboard interaction.

• Examples: Microsoft Windows GUI; Apple Mac OS GUI with UNIX kernel; Unix/Linux with optional GUI.

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Program Execution and System Calls

• Systems must load and run programs, managing the execution process.

• Typically use high-level languages to access OS services via APIs.

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System Calls in Detail

• Each system call associated with a number; the interface invokes it via a kernel call and returns results.

• Programmer follows the API without needing to know implementation details.

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System Call Execution Process

• Flow: User application -> System call interface -> Kernel Mode implementation.

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Example: Standard C Library

• Simple program example using standard library for output.

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System Calls: Windows and Unix Examples

• Process Control: CreateProcess() (Windows) vs. fork() (Unix).

• File Management: CreateFile() vs open().

• Device Manipulation: SetConsoleMode() vs ioctl().

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Types of System Calls

• Process control: create, terminate, load, execute processes.

• File management: create, delete, open, close files.

• Device management: request/release devices, I/O operations.

• Information maintenance: get/set system data.

• Communications: create/delete connections, send/receive messages.

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System Programs

• Known as system utilities, providing a programming environment.

• Can act as user interfaces to system calls or more complex services like device drivers.

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Categories of System Programs

• File management: create, delete, or manipulate files.

• Status information: retrieve system stats like memory or disk space.

• File modification: text editing and transformations.

• Programming-language support: compilers, assemblers, debuggers.

• Program loading/execution: loaders, linkers, debuggers.

• Communications: mechanism for virtual connections and information exchange.

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Process Management Overview

• A process is an executing program needing resources like CPU time and memory.

• Acts as the unit of work within systems comprising both user and OS processes.

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Understanding Processes

• A process is created, scheduled, and maintained with various resource allocations.

• OS roles: creation, deletion, scheduling, synchronization, communication, and deadlock handling.

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Viewing Currently Running Processes

• Windows: use cmd (tasklist) or task manager.

• Unix-like OS: use terminal (ps) or activity monitor.

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Process Concept

• Definition: A process is a job, task, or user program in execution.

• Transitions from executable program to process upon loading.

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Composition of a Process

• Text: Program code, current activity, program counter value, CPU registers.

• Stack: Temporary data (function parameters, return addresses).

• Data: Global variables.

• Heap: Dynamically allocated memory during runtime.

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Process State Changes

• States: New, running, waiting, ready, terminated.

• Only one process can be running; many can be ready or waiting.

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Process Control Block (PCB)

• Represents a process in the OS containing various vital information (state, program counter, CPU registers, etc.).

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PCB Updates

• PCBs are updated whenever a process changes state.

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CPU Process Switching Example

• Shows process state changes when a process stops running.

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Process Scheduling

• The scheduler chooses processes for CPU execution while keeping track of queues: job queue, ready queue, device queue.

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Process Scheduler Queues

• Detailed representation of PCB management in different queues including ready and device queues.

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Scheduler Queuing/Lifecycle Diagram

• Diagrams showing the process life cycle transitions among states (New, Ready, Running, Waiting, Terminated).

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Example: Process "Life" Lifecycle

• Illustrates process transitions through various states during execution.

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Types of Schedulers

• Short-term Scheduler: Decides next executed process, invoked frequently; must be fast.

• Long-term Scheduler: Controls process introduction into ready queue, invoked less frequently; may be slow.