What is an Operating system 

Operating system goals: 

Computer System Components 

  1. Hardware - provides basic computing resources (CPU, memory, I/O devices). 
  2. Operating system - controls and coordinates the use of the hardware among the various application programs for the various users. 
  3. Applications programs - define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business pro grams). 
  4. Users (people, machines, other computers). 

  5. Graphic1 

Operating System Functions 

Early Systems - bare machine (early 1950s) - First Generation.

Simple Batch Systems - Second Generation.


  1. How does the monitor know about the nature of the job (e.g., Fortran versus Assembly) or which program to execute? 
  2. How does the monitor distinguish 
    a) job from job? 
    b) data from program? 

Solution: introduce control cards 

Control Cards 

Spooling - overlap the I/O of one job with the computation of another job. 

(Simultaneous Peripheral Operation On Line) Simple Multiprogramming.

Multiprogramming and Time Sharing- Third Generation 


OS Features Needed for Multiprogramming 

Time-Sharing Systems- Interactive Computing 

Personal-Computer Systems - Fourth Generation

Parallel Systems - multiprocessor systems with more than one CPU in close communication. 

Distributed Systems - distribute the computation among several physical processors. 

Real-Time Systems