Mainframe Systems

First commercial systems: Enormous, expensive and slow, I/O: Punch cards and line printers.

• Single operator/programmer/user runs and debugs interactively:
  • Standard library with no resource coordination
  • Monitor that is always resident
    • initial control in monitor
    • control transfers to job
    • when job completes control transfers back to monitor
• Inefficient use of hardware: poor throughput and poor utilization
• Performance metrics:
  Throughput: like amount of useful work done per hour
  Utilization: keeping all devices busy
• Mainframe systems started to appear after world war 2.
• They initially executed one program at a time and were known as batch systems.