Protection

Pre-emption

• Ability to give and take away resources
• Have periodic timer Interrupts
  • If a process used up quantum (small amount of time allowed to run) → schedule another

Interposition or Mediation

• OS is between application and resources
• Track all resources available for an application
  • E.g. in table
• For each access attempt, check if it is legal in the table

Privileged and Unprivileged modes

• User applications have unprivileged access/user mode
• OS has privileged access/kernel mode