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

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

• OS's first job is to load itself into RAM
  • Called booting.

Booting: six steps

• 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.

• 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.

• 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.

• 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.

• 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.

• Antivirus software
• Speaker volume control
• Etc.

• Final part of booting is to facilitate user authentication or login.
• Typically a user name and password or fingerprint scan or special code.

• 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.

• The OS
  • gives each program a portion of RAM memory.
  • keeps them from interfering with each other.

• 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.

• 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.

• Applications access input and output devices via the OS.
• Device drivers enable communication between the OS and input and output (and other) devices.

• The user interface allows the user to:
  • Start application programs
  • Manage storage devices
  • Safely shut down the computer
  • Perform other interactions

a) graphical, b) menu-driven, and c) command-line user interfaces

• 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.