Definition of an Operating System

Management layer between user and the hardware.

Objectives of OS:

• Run user programs
• Facilitate access to all computer components
• Handle resources and tasks efficiently

System Components

• Process management
• I/O handling
  • Buffer
  • Interface for device drivers
  • Drivers for specific hard ware devices
• Main memory management
• Secondary storage management
  • Tracking of free space
  • Space allocation
  • Scheduling of disk I/O queries
• File management
  • File/directory creation, deletion and manipulation
  • Backup of files on a non-volatile storage media (secondary storage)
• Networking
  • Management of port and network addresses for applications
  • Management of communication protocols
  • Management of machine addresses
• Security management
  • Identify authorized and unauthorized accesses
  • Specify the policies to enforce
  • Provide the means to enforce them
• Command interpretation
• System calls: interface between process and OS
  • Parameter passing via a table

OS Evolutions

• Mainframes
  • Resident monitor
  • Grouping tasks with similar needs
  • Automate sequencing of executions
  • Automatic transfer of control from one task to another
• Batch systems
• Batch multi-program systems
• Timesharing systems
• Personal systems
• Multi-processor systems
• Distributes systems