What is persistence?

• Data is persistent when stored on a permanent medium.
  • Must survive program termination.
  • Must survive computer shutdown.
  
  
• The data may be read by independently executing programs.
  
  
• The data may be added/updated by independently executing programs; coordination required.
  
  
• Manydifferent kinds of technology
  • Hard disks (most common today)
  • Optical CD's
  • Floppy disk
  • Magnetic tape
  • Other technologies exists and new will probably be invented.