• AN operating system (OS) is the software that manages resources of a computer and the sharing of those resources.
• An OS manges memory, processes, files and devices. It also may manage the network connection. It provides a user interface and a programmer interface.



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• OS:
• SW or HW?
• Where is it?
• How does it get there?
• Where does it go when programs execute?
• How is the IP used by OS to launch programs?
• How is the stack used by the OS? (return 0;)



   --------------------------------------------------------------
   Application software
      .system calls: pid = getpid();
         ..kernel: internals that do all you see and don't see
      .system utilities: ls, cd, cat
         ..system calls
            ...kernel

   UI: Shell (Unix) Command line(DOS) GUI (Windows)
      .system utilities
         ..system calls
            ...kernel

==========================================================================!

The system utilities lie below the application layer.
   user-accessible programs
   tools such as ls, ps, od
========================================================

A system call is just what its name implies -- a request for the
operating system to do something on behalf of the user's program.
   functions used in the kernel itself
   appears as a normal C function call
   manage the file system
   control processes
   provide interprocess communication (IPC)
========================================================

The kernel provides the essential services that make up the
heart of UNIX systems
   allocates memory
   keeps track of the physical location of files
   loads and schedules and executes binary programs
==========================================================================!
   

Batch Systems:
. Relied on punched cards or tape for input in past
  Efficiency was measured in throughput (jobs per hour)

Real-time operating systems (RTOS):
. Control machinery, space flights, airport traffic control
. Little user-interface capability -  no end-user utilities
. Manage the resources of the computer so any operation
  executes in same amount of time every time - Not slower - OR faster!

Single-user, single-tasking operating system:
. Manage the computer so that one user can do one thing at a time
  DOS

Single-user, multi-tasking operating system:
. Interrupts allow resource sscheduling
  Windows and the Mac O.S.

Multi-user operating systems:
. Allows many users to use computer's resources simultaneously
. Balance  needs of users
  Ensure all users have what they need
  Protect users from each other
. Unix, VMS

Embedded Systems:
. Computers placed inside products to add features and capabilities
  NO OS or small kernel
 

 1940's
   No standard OS software => machines poorly utilized
   Program included every instruction needed by computer to perform tasks
   Programmer loaded and ran software
   Computer time scheduled like a conference room: 9-10am: Bill Johnson
   


1950s
   Emphasis on cost effectiveness: expensive time lags between CPU and I/O
   Computers were still very expensive: IBM 7094 was priced at $200,000
   Two improvements:
      Computer operators
      Job scheduling: group together programs with similar requirements
   devices
   --------------------------------------------------
   GM, SAFE: main function was to automatically execute a new program

1960s
   Faster CPUs, but their speed caused problems
   Multiprogramming allowed loading many programs at one time
   Program scheduling
   OS taking over functions of operator
   -----------------------------------------------------
   OS/360, IBM:    batch, REQUIRED DASD
   Fred Brooks - Mythical Man Month

 1970s
   Multiprogramming schemes to increase CPU use were limited by
   physical capacity of main memory - solution? VM
   ----------------------------------------------------
   VMS - 32 bit virtual address!
   Microcomputer OSs: CP/M, Apple DOS

 1980s
   Improvement in the cost/performance ratio of computer components
   Hardware became more flexible
   Introduction of multiprocessing-allowed executing programs in parallel
   Evolution of personal computers and high-speed communications
   Introduction of distributed processing and networked systems
   -----------------------------------------------------
   MS-DOS, Windows, Mac OS, Unix

1990s
   Demand for Internet capability sparked networking capability
   Increased networking: tighter security
   Multimedia applications: additional power, flexibility,
    and device compatibility OS
   -----------------------------------------------------------
   Linux, Windows 95/98, Unix
   

   
   

 

Essential managers of an operating system:
  Memory Manager
  Processor Manager
  Device Manager
  File Manager
  User Command Interface is unique to each OS
     GUI
     Command

Each subsystem manager must perform the following tasks:
  Monitor its resources continuously
  Enforce the policies: who gets what, when, and how much
  Allocate the resource when it’s appropriate
  Deallocate the resource when appropriate