IT 209 • MIDTERM REVIEWER

• Operating system

  • program that acts as an intermediary between a user of a computer and the computer hardware.
  • software responsible for the management and coordination activities and and the sharing of the resources of the computer.
  • use the computer hardware in an efficient manner.
  • its job is to coordinate the execution of all other software, mainly user applications.
• Operating System

  1. user
  2. application
  3. operating system
  4. hardware
• the computer system

  HARDWARE 


  provides basic computing resources
• the computer system

  OPERATING SYSTEM 


  controls and coordinates use of hardware among various applications and users.
• the computer system

  APPLICATION PROGRAMS 


  define the ways in which the system resources are used to solve the computing problems of the users. (word processors, compilers, web browsers, database system, video games)
• the computer system

  USERS 


  people, machines, other computers
• computer system


  made up of various components. the components can be hardware or software
• CPU 


  electronic circuit responsible for executing the instructions of a computer program
• registers


  high speed storage areas in the CPU. all data must be stored in a register before it can be processed
• ALU 


  allows arithmetic(add, subtract, etc) and logic(and or not) operations to be carried out
• control unit 


  provides the timing and control signals required by other computer components
• buses


  data is transmitted from one part of a computer to another, connecting all major components to the CPU and memory
• von neumann architecture 


  all temporary computer design are based in this
• components of a modern OS


  USER INTERFACE

  storage management

  device management

  memory management

  file management

  process management
• process management 


  the os must ensure that each running application (process) is treated fairly in terms of processor time allocated in a multi-tasking environment
• storage management 


  must be managed by the operating system, and is the lowest
• memory management

  • can neither run into the memory space of another process nor be run into by another process.
  • must be used properly so that each process can run most effectively
• device management


  managing input and output is largely a matter of managing queues and buffers
• file management


  method for storing and organizing computer files and the data they contain to make it easy to find and access them.
• user interface

  • set of commands or menus through which a user communicates with a program
  • "shell"
  • command driven or graphical user
• OS Service: program execution


  able to load a program into memory and to run that program, end execution, either normally or abnormally(indicating error)
• OS Service: resource allocation


  when multiple users or multiple jobs running concurrently, resources must be allocated to each of them
• OS Service: i/o manipulation


  running program may require i/o, which may involve a file an i/o device
• OS Service: communication


  process may exchange information
• OS Service: error detection 


  needs to be constantly aware of possible errors
• OS Service: accounting 



  to keep track of which users use how much and what kinds of computer resources
• OS Service: protection & security

  • protection - ensuring that all access to system resources is controlled
  • security - outsiders requires user authentication
• system calls 


  • program to request service from the operating system

  • way for programs to interact with the operating system
• services provided by system calls

  -process creation and management

  -main memory management

  -file access, directory and file system management

  -device handling(i/o)

  -protection

  -networking
• types of system calls: process control


  end & abort

  load & execute

  create process & terminate process

  wait & signed event

  allocate and free memory
• types of system calls: file management


  create

  open

  close

  delete

  read file
• types of system calls: device management


  device manipulation like reading from device buffers, writing into device buffers
• types of system calls: information maintenance


  handles information and its transfer between the OS and the user program
• types of system calls: communication


  specially used for interprocess communications
• kernel


  primary interface between the hardware and the processes of a computer.

  it is named kernel because it operates inside the OS, just like seed inside a hard shell
• wait()


  process needs to wait for another process to complete its execution
• fork()


  to create processes that are a copy of themselves
• exec()


  run when an executable file in the context of an already running process that replaces the older executable file
• kill()


  used by the OS to send a termination signal to a process that urges the process to exit
• exit()


  used to terminate program execution