Unit 9

• If there is no OS

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  • Computers can only run 1 program at a time
  • Cannot control peripheral devices
  • No user interface
  • No facility to store, retrieve, and manipulate files
• Basic services of OS

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  • Accepts commands and requests from users and their programs. It will respond with appropriate output results
  • Manages, loads, and executes programs
  • Manages hardware resources of a computer
• Concurrent OS operations

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  • Multitasking
  • Multiprocessing
• Examples of other OS services

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  • Provides users with an interface and command execution
  • File management
  • I/O services
  • Process control management (scheduling, multitasking)
  • Memory management
  • Secondary storage and security
  • Network and communication services
• 3 main parts of an OS

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  • Memory resident - a program or portion of a program that remains in the computer's main memory for immediate use
  • Memory non-resident - this refers to a program or data that is not stored in the computer's main memory, it may need to be fetched from the secondary storage when needed for execution
  • Bootstrap - a process that initializes a computer's hardware and software components to start the OS
• Some categories of OS

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  • Single-user, single tasking (essentially obsolete)
  • Single-user, multitasking
  • Mainframes
  • Network servers
  • Distributed and real-time systems
  • OS for mobile devices
  • Embedded systems
• Degree of activity

  How OS interact and behave with the user

  
  

  Types of activity:

  • Interactive (conversational systems) - interacts with the user when the user requires or gives commands
  • Batch processing - user submits programs or jobs for processing, it will all be executed at once (little to no user monitoring)
  • Event driver - only acts when an interrupt occurs
• Secondary storage and security

  Secondary storage management:

  • Optimizes completion of I/O tasks for efficient disk usage

  Security and protection services:

  • Protects OS from users
  • Protects users from other users
  • Prevent unauthorized entry and use of the system
• Network and communication services

  TCP-IP protocol suite makes data exchange between 2 devices possible. It specifies how data should be packetized, addressed, transmitted, routed, and received on a network
• 3 main OS organization configurations

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  1. Monolithic config
  2. Hierarchical (layered) config
  3. Microkernel
• Monolithic (config) kernel

  The OS works in a kernel space

  Stability and integrity must be managed carefully
• Hierarchical model

  Each layer is independent of the other layers. Requests are passed down a layer immediately below it
• Microkernel config

  Provides the most basic services required for an OS to function, e.g memory management and process scheduling