Operating System Fundamentals (Cambridge (CIE) A Level Computer Science) : Revision Note

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 MSDOS (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 MAC OS

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

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

• Inputs/outputs 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) in to small chunks and allocating them to different processes

• The CPU can only execute one process at a time, it can can execute billions of them in one second

• The OS uses a scheduling algorithm to prioritise processes

• Processes are placed in queue whist 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)