/operating-systems-concepts

Notes from Operating System Concepts

Primary LanguageC

Operating System Concepts

Basics

type of os:

  • batch
  • time sharing
  • single user
  • multi user
  • distributed
  • real time
  • general purpose

interrupt

Overview

  • System Calls
  • System Programs
  • OS Design
    • policy vs mechanisms

critical modules that require high performance

  • interrupt handler
  • i/o manager
  • memory manager
  • cpu scheduler

two common models of ipc (inter process communication)

  • message passing
  • shared memory

virtual connections between processes, users, computer systems

Background Services are called services / subsystems / daemons

Operating Systems Structure

  • MS-DOS
  • Unix

Kernel Provides

  • File System
  • CPU Scheduling
  • Memory Management

Layered OS

  • One Problem - Overhead system calls
  • Another Problem - Designing Layers Order
  • Fewer Layers with More Functionality

MicroKernel - All Non Essential Parts are moved to system programs and User Space Mac OSX Darwin is also partly based on the Mach MicroKernel

Loadable Kernel Modules - Linking service dynamically

  • Architecture of Mac OSX
  • Architecture of iOS
  • Architecture of Android

OS Debugging

  • Log File
  • Core Dump
  • Crash
  • Crash Dump

What Kernel Do in unrecoverable situation? Save Kernel's Memory state to a section of disk that does not have any FileSystem. When Kernel encounter a unrecoverable error, it take it's entire content of memory or kernel owned part and dump it into disk section. when booting, a process runs and tries to gather the memory dump from the disk and save it as file in filesystem

Trace Listing

System Generation

  • CPU
  • Boot Disk
  • Memory
  • Device
  • OS Options

System Boot

  • initial bootstrap program

Process Management

process

job == process == cpu_activities

  • processs in memory

    • text (code/instructions)
    • data (global vars)
    • heap (dynamically allocated)
    • stack (temporary data - function params, return addresses, local vars) process-in-memory

  • a process itself can be execution environment

    • jvm is a process (which takes java code and take actions via native machine instructions on behalf of that code) job == process == cpu_activities

Process State

  • new - created process
  • ready - ready to be assigned to processor
  • running - instructions are being executed
  • waiting - waiting for an event to occur (I/O Completion or reception of a Signal)
  • terminated - finished execution

Scheduling Queues

  • job queue
  • ready queue
  • device queue

once the process is allocated to CPU one of the following events may occur

  • process issuing I/O request -> I/O Queue -> I/O Happens -> then it placed into the Ready Queue Again (does it stay all the time in CPU if not is it immediately moved to Ready Queue?)
  • Time Slice Expired -> Moved to Ready Queue
  • Fork A Child -> wait for child's termination
  • Wait for an interrupt -> Interrupt Occurs -> then it process from Ready Queue

Process Termination

  • removed from all queues

  • PCB(process control block) and resources deallocated

  • single threaded vs multithreaded process

When a request is made, rather than creating another process, the server creates a new thread to service the request and resume listening for additional requests.

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