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====== Operating System Fundamentals ======

Adapted from:\\
LaBerta, Catherine. "System Software." In //Computers Are Your Future.// 11th ed. Boston: Prentice Hall., 2010

Mithat Konar\\
Dec. 4, 2019

===== The Operating System =====

  * The **operating system** (OS) is a set of programs that coordinates:
    * Hardware functions
    * Interaction between application software and computer hardware

===== The Operating System =====

  * Five basic OS functions:
    * Starting the computer
    * Managing applications
    * Managing memory
    * Handling input and output device messages
    * Providing a user interface for communication

===== OS function 1: Starting the computer =====
  * OS's first job is to load itself into RAM
    * Called **booting**.

===== OS function 1: Starting the computer =====

{{:computer_basics:ch04-booting.jpg?direct&300|}}\\
Booting: six steps

===== Booting step 1: BIOS and EFI =====

  * Many computers use a **BIOS (Basic Input/Output System)** to begin the booting process.
  * The first thing that is loaded into memory and starts running when you turn on.
  * Manages some core hardware settings.
  * Handles the very first stages of the booting process.
  * Usually stored in flash memory or CMOS memory chip.

===== Booting step 1: BIOS and EFI =====

  * Most newer desktops and laptops use **EFI (Extensible Firmware Interface)** instead of a BIOS.
    * ** UEFI (Unified Extensible Firmware Interface)** is one example.
  * Like a mini OS.
  * Does everything BIOS does.
  * Lets user run small utility applications that run on the Extensible Firmware Interface.
  * Considered more secure than traditional BIOS.

===== Booting step 2: Test the hardware =====
  * Many BIOS/EFIs initiate a **power-on self-test (POST)** or similar test.
  * Confirms that both the computer and its peripheral devices are working properly.

===== Booting step 3: Load the operating system =====
  * BIOS or EFI loads an OS's **kernel** into memory.
    * kernel: the central part of the OS.
    * Usually stored on main storage device.
  * The OS then loads remainder of what's needed.

===== Booting step 4: Check the system configuration =====
  * The OS checks the system configuration for **device drivers**.
    * device driver: utility program that enables communication between the OS and a peripheral device.
  * The OS installs and loads the needed drivers.

===== Booting step 5: Load system utilities =====
  * Antivirus software
  * Speaker volume control
  * Etc.

===== Booting step 6: Authenticate user =====
    * Final part of booting is to facilitate user authentication or login.
     * Typically a user name and password or fingerprint scan or special code.

===== OS function 2: Managing applications =====
  * **Multitasking** operating systems permit more than one application to run at the same time.
    * The **foreground application** is the active one.
    * The **background applications** appear inactive.

===== OS function 3: Managing memory =====
  * The OS
    * gives each program a portion of RAM memory.
    * keeps them from interfering with each other.

===== OS function 3: Managing memory =====
  * RAM is organized into **pages**: units of large fixed size.
  * **Virtual memory** uses a portion of the hard disk to extend RAM.
    * When RAM is full, the contents of the most inactive page or pages are temporarily moved to a **swap file**, a special hard disk file.
    * When the page is again needed, it is transferred back into RAM.
    * Transferring files between RAM and the hard disk is called **paging**.

===== Virtual memory =====
{{:computer_basics:ch04-virtualmemory.jpg?direct&600|}}

===== OS function 3: Managing memory =====
  * Adding more RAM is often a good way to improve computer performance because:
    * Paging slows the computer.
    * Accessing data from the hard disk is slower than accessing it from RAM.

===== OS function 4: Handling input and output =====
  * Applications access input and output devices via the OS.
  * Device drivers enable communication between the OS and input and output (and other) devices.

===== OS function 5: Provide a user interface =====
  * The **user interface** allows the user to:
    * Start application programs
    * Manage storage devices
    * Safely shut down the computer
    * Perform other interactions

===== User interfaces =====
{{:computer_basics:ch04-userinterfaces.jpg?direct&600|}}\\
a) graphical, b) menu-driven, and c) command-line user interfaces

===== OS function 5: Provide a user interface =====
  * Types of user interfaces:
    * **graphical user interface (GUI)** uses **icons** and other visual metaphors.
    * **menu-driven interface**:
      * Provides text-based menus.
      * Displays available user options.
    * **command-line interface**:
      * Requires the user to type commands to instruct the OS to perform the desired actions.