evolution of OS and Computer Generation

Generations:

1. 1945 ~ 1955: Vacuum Tube, Plug boards
   
2. 1955 ~ 1965: transistors
   the primitive concept of OS appeared, known as Batch System
   actually, the concept of batch system originally are from the assembly line
   and was first implemented to punched card systemthen came to the
   popular command line interface today on workstations, but the difference
   is that only one process, one shell running, tasks must be done
   one after another(batch)
   
3. 1965 ~ 1980: ICs
   since the complexity of computing is rising ICs became more and
   more popular after it's creation
   
   the concept of OS, has evolved almost completely at this stage:
   batch -> Multiprogramming -> Time Sharing
   Multiprogramming:
   
   • on Batch system, we can only do one thing at a time, then people
     came to think about the possibility to do several things altogether
     the concept of scheduling appeared.
     we create several processes and use scheduler take turns
     to running each of them. Since the CPU is so fast that it seems
     that they are running concurrently.
     
   Time Sharing:
   
   • the evolution is the appearance of Round-Robin algorithm
     in the past, processes are non-preemptive(cannot be interrupt)
     so once u encounter a long job, user will be hanging. Round-Robin
     introduce the concept of Time Quantum. once Quantum
     expired, contex switch
     
4. 1980 ~ present: PC
   at this time Main Frame computer being replaced by Personal Computer
   the concept of Operating System are the same but the resources are
   different
   eg. in the past, Main Frame Computer can assign special resource like
   graphic card to some special user