Operating System fundamentals (Cambridge International AS Computer Science)

Purpose of an OS

What is an operating system (OS)?

• An operating system (OS) is software that provides an interface between the user and the hardware in a computer system

• An operating system hides the complexities of the hardware from the user, for example:

  • A user does not need to know 'where' on secondary storage data is kept, just that it is saved for when they want it again

• To help achieve this an OS provides a user interface

User interface

• A user interface is how the user interacts with the operating system

• Examples of user interfaces include:

  • Command Line Interface (CLI)
  • Graphical User Interface (GUI)
  • Menu
  • Natural language (NLI)

What is a command line interface (CLI)?

• A Command Line Interface (CLI) requires users to interact with the operating system using text-based commands
• CLIs are more commonly used by advanced users
• Examples of CLIs are MS-DOS (Microsoft Disk Operating System) and Raspbian (for Raspberry Pi)

What is a graphical user interface (GUI)?

• A Graphical User Interface (GUI) requires users to interact with the operating system using visual elements such as windows, icons, menus & pointers (WIMP)
• GUIs are optimised for mouse and touch gesture input
• Examples of GUIs are Windows, Android and macOS

What is a menu interface?

• A menu interface is successive menus presented to a user with a single option at each stage

• Often performed with buttons or a keypad

• Examples include:

  • Chip and pin machines
  • Vending machines
  • Entertainment streaming services

What is a natural language interface (NLI)?

• A natural language interface (NLI) uses the spoken word to respond to spoken or textual inputs from a user

• Examples include:

  • Virtual assistants- Amazon Alexa, Google Assistant, Siri
  • Search engines
  • Smart home devices

OS management tasks

An operating system has five key management tasks:

• Memory management
• File management
• Security management
• Hardware management
• Process management

Memory management

• Memory management is a process carried out by the operating system allocating main memory (RAM) between different programs that are open at the same time

• The OS is responsible for copying programs and data from secondary to primary storage as it is needed

• Programs and data require different amounts of RAM to operate efficiently and the OS manages this process

• RAM is allocated based on priority and fairness, for example, system applications (essential) may have a higher priority than user applications

• The OS dynamically manages the memory, adjusting allocation as needed to maintain optimal system performance

• Memory management makes multitasking possible

  • Prevents data from different programs overwriting each other in RAM
  • Decides which processes and data should be kept in main memory at any given time

File management

• File management is a process carried out by the operating system creating, organising, manipulating and accessing files and folders on a computer system

• The OS manages where data is stored in both main memory and secondary storage

• File management gives the user the ability to:

  • Create files/folders
  • Name files/folders
  • Rename files/folders
  • Copy files/folders
  • Move files/folders
  • Delete files/folders

• The OS allows users to control who can access, modify and delete files/folders (permissions)

• The OS provides a search facility to find specific files based on various criteria

Security management

• Operating systems provide various security features such as password-protected system accounts, a firewall, virus scanning and file encryption
• Password-protected system accounts are a very common feature in operating systems
• A system administrator is able to allocate different access rights for different users on a network
• The OS is able to maintain settings for individual users, such as desktop backgrounds, icons and colour schemes
• The OS audits(keeps a log of) files created by users, accesses, edits and deletes

Hardware management

• Peripheral management is a process carried out by the operating system managing the way peripherals (hardware) interact with software
• The OS allocates system resources to peripherals to ensure efficient operation
• Peripheral management makes plug-and-play (PnP) functionality possible, automatically detecting and configuring new peripherals without the need for manually installing device drivers or power cycling the system
• A device driver is a piece of software used to control a piece of hardware
• Input/output devices require device drivers in order to be used by the operating system
• The OS has generic device drivers built in which makes basic compatibility possible
• In order for hardware to be used to its maximum capacity, often a separate device driver must be downloaded from the manufacturer
• Device drivers are OS specific and are regularly updated

Process management

• Process management is a process carried out by the operating system dividing time (time slicing) into small chunks and allocating them to different processes
• The CPU executes one instruction at a time, but rapid context switching allows multiple processes to share processor time
• The OS uses a scheduling algorithm to **prioritise **processes
• Processes are** placed in queue** whilst waiting to be carried out, they return to the back of the queue when their time is up
• The goal of process management is to share resources (CPU & main memory)
• Allows processes to be paused and resumed using context switching
• Decides which process is executed next using a scheduling algorithm

Worked Example Identify four key management tasks that the Operating System will perform. [4]

Final answer: Answer

• Memory management [1 mark]
• File management [1 mark]
• Security management [1 mark]
• Hardware / device / peripheral / resources management [1 mark]
• Input/output management [1 mark]
• Process management [1 mark]
• Error checking and recovery [1 mark]
• Provision of a platform for software [1 mark]
• Provision of a user interface [1 mark]