Section 11.5
Review Questions
OS Modes and instructions
  1. What are the two modes that operating systems must provide in order to protect the system?
  1. What kind of hardware is needed to determine the current mode of the CPU?
  1. Who can change the mode?
  1. Define trap.
  1. What term does IBM use for trap?
  1. List some of the tasks of an operating system.
  1. What term do we use for a subroutine in the operating system that is meant to provide a service to user programs?
  1. If subroutines in the operating system are privileged, how does a user program ever call them?
  1. What does Unix call the user that has full privileges?
  1. Why is the CAL instruction dangerous is an otherwise secure computer system?
  1. How is the TRP instruction different from CAL?
  1. What is abend a contraction of?
  1. What is the first thing that an operating system call does when it is called by a user program?