Objectives

1. Discuss the services provided by an operating system from several different perspectives.
2. Describe different forms of user interface.

Notes

• Last chapter we discussed how an os can be viewed many different ways.
• This chapter focuses in on what the authors intend us to study.
• This is section 2.1, read it.
• Figure 2.1 on page 56 is worth a quick glance.
• What does the OS do for the user
  • The user interface.
  • Program execution
  • File System (manipulation)
  • Communications
    • Between processes on the same machine
    • To other machines
    • Two ideas
      • Shared memory, multiple processes can read/write to the same memory
      • Message Passing
    • But this implies synchronization and some locking mechanism.
  • Error Detection
    • Which again implies some form of communications.
• What about from a system operation view?
  • Resource allocation
    • CPU, memory, file space, device, ...
  • Logging
    • Keeping track of what is happening
    • For security, billing, or even error detection/correction
  • Protection and security
• The next section discusses user interfaces.
  • This is section 2.2. Read it as well
  • They break user interfaces into three big categories
    • Command line interfaces
    • Graphical User Interface
    • Touch Screen Interface
  • I would propose voice command interface as well.
  • All have the commonality of making the computer system usable.
  • Command line interfaces
    • Usually through a command interpreter
    • They say a shell is a command interpreter on a system with choices
      • On linux/unix
        • you probably use the Bourne Again shell (bash)
        • This came from the Bourne Shell (sh),
          • Written in the 70s by Stephen Bourne at Bell Labs.
      • Others include
        • csh - c shell (c like control structures)
        • ksh (Korn shell, written by David Korn, like sh)
        • busybox, aimed at embedded boxes, but some people love it.
        • Many others, some semesters we write a partial shell in systems programming.
    • Shells allow/support
      • Shell scripts, or programs that are executed by the shell.
      • This includes
        • Control structures
        • Variables

        • for f in ../ch1/*
          do
             wc $f
          done

      • I/O redirection
      • Define a working environment (envp)
      • Customization of user experience.
      • Process control: starting, stopping, suspending, ...
    • Two approaches
      • The shell has many built in commands, the shell provides all interaction with the os.
      • The system provides all commands, the shell finds these and executes them.
    • Linux/Unix can do either of these.
      • Bash supports pushd, popd: to change directories, but store the old one on the stack.
      • But most commands are in /bin or /usr/bin
        • whereis command
        • which command, for me which is a highly customzed alias.
    • Shells are highly complex tools, I totally underuse bash.
  • GUI
    • First developed in the 1970s at Xerox Parc (Xerox's research lab)
    • Windows
    • X in the Unix world.
      • Like the shell, this is not part of the kernel
  • Does the touch screen deserve a separate classification?
• I enjoyed the justification for using cli.