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Operating Systems - History of Operating Systems & Basic Operating System Concepts [Class Notes]

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A Brief History of Operating System [Class Notes]

History of Operating Systems
Basic Operating System Concepts


Suresh Khanal
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What is an Operating System?

An operating system should be conceived as a combination of following different aspects:-

1. A Program
but with a funny function invocation mechanism. An operating system is no different than any other program, other than it lays on the bottommost layer.

2. A Control Program

controls the execution of programs and devices. An operating sytem is responsible to monitor and control the operation of each and every software as well as hardware components of a computer system.

3. An Interface

An abstract virtual machine. Operating system behaves as a computer system for all other applications so that the communication is possible and the underlying hardware details are encapsulated to provide common standard interface.

4. A Programming Environment

The kernel + utilities

5. A resource manager

The operating system maximizes system performance since it manages the available resources.

6. A service provider

An operating system provides different services to other applications such as File storage, network communications, and so on.

Why do we need operating system?

Today it would appear a funny question. We can't imagine operating a computer without an operating system. But, major reason can be drawn as following two:-

1. They Provide a high-level abstraction of physical resources

Since operating systems provice common standard interface, it enables the construction of more complex software systems. Similarly, without operating system, it would be impossible to imagine portable code.

2. They allow sharing of limited or expensive physical resources

Because operating systems manages the computer resources it is possible to share the expensive physical resources and optimize their use.

A Brief History of Operating Systems

Hand Programmed Machines ('45-'55)

  • Single Usser Systems
  • OS = loader + libraries of common subroutines
  • Drawback: low utilization of expensive components

Batch Processing or Offline processing ('55-'65)

  • Pipelined processing of jobs. (Overlap computation with I/O)
  • Utilization is higher
  • But throughput is low. [throughput=(number of jobs completed)/(observation interval)]
  • Operating System = loader + sequencer + output processor 

Spooling Processing or online processing ('62-'69)

  • Disks/drums enabled overlap of I/O and computation on the same machine
  • Utilization is higher
  • And at the same time throughput too improved

Multiprogramming ('65-'80)

  • Keeps several jobs in memory and multiplex CPU between jobs
  • Simple, synchronous input. This solved the problem of 'what to do while waiting for the I/O device?'

Timesharing('70-  )

  • A timer interrupt is used to multiplex CPU among jobs

Types of Operating Systems

Personal Computing System

  • Single user
  • Utilization is no longer a concern
  • Emphasis is on user interface and API
  • Many serices and features are not present
  • Primary concern in personal computing system is response time [ response time = completion time - start time]

Distributed Operating System

  • Typically support distributed services
  • Possibly employ multiple processors (loosely coupled vs. tightly coupled systems)
  • High availability and reliability requirement

Parallel Operating System

  • Symetric Multiprocessing

Each processor has a copy of the operating system. Many jobs can be executed in parallel.

  • Asymmetric multiprocessing

Master processor allocates jobs to slave processors

Real-time Operating System

  • A system with a dual notion of correctness:
    • Logical correctness - "It does the right thing"
    • Temporal correctness - "It does it on time"
  • A system wherein predictability is more important than performance
  • Dedicated system: real-time performance achieved iff time(loop)<= 33ms. Realtime computing is a programming problem ("Just buy a faster processor")
  • Multiprogrammed system: real-time performance iff ??? Real time computing is an operating system problem.



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