Introduction Part 1

• This is based on chapter 1.1 of the book.
  • You should read this.
• And my knowledge:
  • Which is heavily UNIX/Linux biased.
• An Operating System is a program that manages the computer's hardware.
  • I like: Manages the resources of a computer.
  • These include
    • CPU/processors/cores/... time
    • Memory
    • Secondary storage
    • I/O devices
• These are not applications for the most part
  • An OS allows you to use an application.
  • But I suppose, on an old game console, ...
• There is quite a diversity in operating systems,
  • Smart watch to full blown multi user-computer systems.
• This means that there is really no "standard" operating system.
  • I tend to be biased towards multi-user multi-processing operating systems.
  • But I bet the single user (phone) operating system probably dominates these days.
• There is a great deal of diversity:
  • The OS on my Amazon Echo Dot.
  • The OS on my Truck.
  • The OS on Mirkwood.
  • The OS on a distributed supercomputer.
  • Can you think of other environments?
  • Think about:
    • the scope of i/o devices each controls.
    • the level of security each must provide
    • the user interface provided
    • Can you think of other items?
  • Each of these is probably constructed in a radically different manner.
  • However
    • Most OS's consist of a program called a kernel.
      • This is the PRIMARY program of the OS.
      • It is responsible for all of the definitions above.
      • It is the OS proper.
    • There are some programs that work closely with the kernel called daemons
      • This is not a proper definition, we will get that later.
      • But I need it for the next points.
      • Not a demon, but a "helpful spirit or guardian angel". (Evi Nemeth)
      • In that sense, a program that is running that provides a service.
      • systemd on a linux os provides utilities to start and stop system services such as the web server (httpd) or the fire wall software (firewalld).
      • But, httpd, for example, might not be a system level application. (but that supports the idea that I am working on right now)
      • By the way, in modern linux, some "daemons" are actually manifestations of the kernel.
    • In addition there are usually a number of systems programs that interact with the kernel
      • Some, like systemctl allow a user to interact with a portion of the kernel or a daemon.
      • Some, like vi allow the user to perform low level system related tasks, like changing a configuration file.
    • Finally, there are application programs.
      • Word, power point, ...
      • But where does the web browser fall?
      • How about the web server?
  • So we see that the definition of an OS is somewhat elusive
    • So I will stick to the definition, a program that manages the resources of a computer.
    • Or perhaps a set of programs used to manage the resources of a computer.