OPERATING SYSTEM Cont..

Role of an Operating Systems :

• All computers rely on an operating system (OS) to provide the interface for interaction between users, applications, and hardware.
• The operating system boots the computer and manages the file system.
• Almost all modern operating systems can support more than one user, task, or CPU.
• The operating system has four main roles:

Control hardware access
Manage files and folders
Provide user interface
Manage applications

Characteristics of Operating Systems

• Control hardware access
  OS automatically discovers and configures PnP hardware
• File and folder management
• User interface
  Command line interface (CLI)
  Graphical user interface (GUI)
• Application management
  Open Graphics Library (OpenGL)
  DirectX

The Types of Operating Systems
1. Command Line Interface (CLI): The user types commands at a prompt.
Ex. DOS
2. Graphical User Interface (GUI): The user interacts with menus and icons.
Ex. Windows 2000, Windows XP etc.,

Compare Operating Systems:

Terms often used when comparing operating systems:

• Multi-user – Two or more users can work with programs and share peripheral devices, such as printers, at the same time.
• Multi-tasking – The computer is capable of operating multiple applications at the same time.
• Multi-processing – The computer can have two or more central processing units (CPUs) that programs share.
• Multi-threading – A program can be broken into smaller parts that can be loaded as needed by the operating system. Multi-threading allows individual programs to be multi-tasked.

Real Mode

• Executes only one program at a time
• Addresses only 1 MB of system memory at a time
• Directly accesses memory and hardware
• Subject to crashes
• Available to all modern processors
• Only used by DOS and DOS applications

Protected Mode

• Has access to all memory
• Can manage multiple programs simultaneously
• Allows the system to use virtual memory
• Provides 32-bit access to memory, drivers, and I/O transfers
• Each program is assigned a space in memory
• Computer is protected from program errors

Virtual Real Mode

• Allows a real-mode application to run within a protected-mode operating system
• Creates virtual machines for each program that runs in real mode
• Each virtual machine receives 1 MB of memory and access to hardware
• In the event of a program error, only the virtual machine is affected

Compare Operating Systems
Desktop operating systems:
Microsoft Windows: Windows XP
Macintosh: Mac OS X
Linux: Fedora, Ubuntu, and others
UNIX
A desktop OS has the following characteristics:
Supports a single user
Runs single-user applications
Shares files and folders on a small network with limited security

Network Operating Systems (NOS)

Common NOS include:
Novell Netware
Microsoft Windows Server
Linux
UNIX
A network OS has the following characteristics:
Supports multiple users
Runs multi-user applications
Is robust and redundant
Provides increased security compared to desktop operating systems