Operating System

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 Introduction to Operating System (OS)
Definition





OPERATING SYSTEMS
  • Is a software that acts as an interface between the user, application software and the computer hardware
EXAPMLE OF OPERATING SYSTEM
  1. Microsoft Disk operating system ( Ms DOS)
  2. Windows ( 98, 2000, XP, vista)
  3. Linux
  4. Unix
PARTS OF OPERATING SYSTEM
  1. Shell – it is the outer part of an operating system and it is responsible of interacting with the operating system
  2. Kernel – Responsible for managing and controlling computer resources such as the processor, main memory, storage devices, input devices, output devices and communication devices
RESOURCE UNER THE OPERATING SYSTEM CONTROL
  • The processor
  • Main memory
  • Input/Output Device
  • Secondary storage devices
  • Communication devices and ports
FUNCTIONS OF OPERATING SYSTEM
  1. Job scheduling
– it is the process of the operating system to keep list of jobs currently being run by the computer and clocking them in and out of the processor.
  1. Interrupt handling
  • It is a break from the normal sequential processing of instructions in a program
  1. Resource control and allocation
  • It is situation where the processor gives a computer resources a unique number called interrupt number so that it can be able to recognize and prioritize it.
  1. Memory Management
  • It is where the operating system constantly assigns main memory storage partitions to data an instructions
  1. Error handling
  • It is a situation whereby an operating system alerts the user of errors that arises in ease of illegal operations, hardware or software failure.
  1. Input/output handling
NOTE
What is interrupt request?
  • Is a unique number that is given to a resource for identification purposes
What is the importance of interrupt computer
  • To enable urgent tasks/ processes to b given the first priority during program execution
What is virtual memory
  • Part of the hard disk that acts as maim memory
  • Operating system organizes the main memory in blocks called page frames. The processes are divided into partitions that can fit in a page. The operatind system swaps these pages between the main memory and the hard disk. The part of the hard disk where these pages are held in the virtual memory.
What is a deadlock
  • Is where a particular task holds a resourcs and refuses to release it for othe tasks to use.
CLASSIFICATION OF OPERATING SYSTEM
They are classified into three ways/types:-
  1. According to the number of tasks handled concurrently
  2. Single task – one task is operated at a any given time
  3. Multi-Task – More than one task is processed apparently simultaneously
  1. According to the number of users
  2. Single user – Single (One) user operates a computer at any given time
  3. Multi user – More than one user can operate the computer at the same time
  1. Human computer interface / G U I
  • Interaction between the computer and the user.
  1. Command line – The user types the commands at the command prompt to activate them by pressing the enter key
Advantages
  • Fast in operation by experienced users
  • flexible
  • Use Less memory
  • Don’t require expensive hardware
Disadvantages
- Hard to learn and understand
- Not user friendly
- If you mistype or forgot the syntax of writing the command, you cannot operate it
- Difficult to learn
- Difficult to move information from one application to another
- Difficult to design and produce printed reports
- Do not support multi-users and multi-task
  1. Menu driven – The user is provided with a list of menu to choose from
Advantages
  • More user friendly than command line
  • More easier to learn and understand
  • Eliminates the problem of forgetting the syntax of command since commands are provided for you
Disadvantages
  • Slow to operate
  • Not flexible
  1. Graphical User Interface(GUI) – The user interacts with the computer using icons and menus and select them using pointer
Advantages
- It is easy to learn and operate
- They make it easy to exchange information between application
- Reduce the user training time and cost due to their inform mode of operation
- It is more user friendly
- Supports multi user and multi task
Disadvantages
  • Cost of GUI supporting hardware is higher
  • Many objects on the GUI confuse new computer users
  • - Require faster processors that are more expensive
WINDOW as used in operating system
Is a rectangular object created on a screen by operating system to contain input or output data for a particular program
PROPERTIES OF A WINDOW
  • Title bar
  • Display/ working area
  • Horizontal and vertical scrolls bars
  • Menu bars
  • Status bar
  • Tool bar
TYPES OF MENUS
  1. Pop up menu
  2. Pop down menu
  3. Sub menu( Cascading/ Side kick menu)
COMPUTER FILES
Are classifies into types :-
  1. System Files
Are files that contain information that is critical to the operations of the computer
  1. Application Files
Are files that holds programs or application files

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