Operating Systems


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What is an Operating System?

An operating system hides the complexity of the computers hardware and makes it useable, it allows control over input and output devices and managing data storage.

A 'Virtual Machine' is just a way of describing the computer the user see's and experiences.

It controls resources such as:

  • Processor Scheduling
  • Memory Management
  • I/O Management
  • File Management

The Operating System also deals with system security and controls the operation of the virtual computing environment.

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Layers of the Operating System

8. User Interface/Application Programming Interface

7. Input/Output management

6.File Management

5. Memory Management

4. Processor Management

3. Device Drivers

2. Kernal

1. Hardware

The Application programming interface allows the program to call on services of the OS.

The Kernal acts as a bridge between the software and the hardware.

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Types of Operating System

Interactive Operating System: A OS where the user and the computer are in direct two way communication

Real-Time Operating System: Inputs are processed in a timely manner so that the outputs effect the source of the input.

- Must be able to deal with API programs that do not have a designated BEGIN and END

- Must be able to deal with a number of events that could happen at unpredictable moments

- They have to be able to carry out a process in a designated time

- Example: An airline reservation system

- Would be used for controlling machinery, scientific instrumens and things that have a limited user interface.

Network Operating System: A layer of software that is added to the OS to allow communication between the computer and the network.

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Types of Operating System Continued..

Desktop Operating Sytem: A general purpose OS that allows a broad rango of tasks to be performed

Client Server System: A System in which computers(Client) will request resorces or services from another computer(Server)

Server Operating System: A OS optimised to do a specific task on a network which is fast as its only dealing with a specific request not many different ones.

Sandbox: A tightly controlled set of resorces for guest programs to run on for example a Java Application on a mobile phone gets a limited amount of resources to use.

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Allocating Processor Time

A processor gives the illusion of multitasking but inreality it can only deal with one thing at a time.

A processor will either:

1. Do one process until its fully completed then move to the next


2. Allocation each process an amount of time an switches between several processes until completed, this is called time slicing

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