The Purpose & Functionality of Operating Systems (Cambridge (CIE) O Level Computer Science)

What is an operating system?

• An operating system (OS) is software that manages computer hardware and provides a platform for running applications

• It provides an interface between the user and the hardware in a computer system

• It 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

• An operating systems main functions can be divided in to eight key areas

File Management

What is 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 primary 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

Handling Interrupts

What is interrupt handling?

• Interrupt events require the immediate attention of the central processing unit

• In order to maintain the smooth running of the system, interrupts need to be handled and processed in a timely manner

• For example, if a user clicks cancel on a file conversion process, a signal is sent from the mouse, interrupts the processor, and the operating system will trigger the cancellation routine

User Interface

What is a 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?

• 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?

• 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?

• 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

Advantages and disadvantages of user interfaces

Peripheral Management & Device Drivers

What is peripheral 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

What is a device driver?

• A device driver is a piece of software used to control a piece of hardware

• Peripherals 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 and enables plug-and-play (PnP)

• 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

Memory Management & Multitasking

What is 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

What is multitasking?

• Multitasking is a process made possible by the OS simultaneously managing system resources (memory, CPU etc) to give a user the perception of being able to use multiple programs at the same time

• The OS splits tasks and allocates system resources based on a priority

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

• This makes it appear that multiple programs are running at the same time

Providing a Platform for Running Applications

• Operating systems provide a platform on which application software can run, this is mainly by allowing software access to system resources

• For example, if a computer game has intensive graphics and online play, the operating system will grant it access to the GPU and the network card

Organisation of application layer, operating system components, and input/output

Providing System Security

What is system security?

• 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

• System accounts can also be restricted from performing certain actions, e.g. editing network settings, installing unapproved software, changing the account settings of other users

User Management

What is user management?

• User management is a process carried out by the operating system enabling different users to log onto a computer

• The OS is able to maintain settings for individual users, such as desktop backgrounds, icons and colour schemes

•  A system administrator is able to allocate different access rights for different users on a network