Operating Systems (OCR A Level Computer Science)

Operating Systems

Why do we need Operating Systems?

• Operating systems are essential for managing the hardware and software resources of a computer system

• They provide an interface between the user and the hardware, allowing the user to interact with the system and run applications

What are the main functions of an operating system?

• Operating systems such as Windows, MacOS, Android, Linux, iOS and Ubuntu have responsibilities that can be grouped into the following categories:

  • Resource management

  • File Management

  • Interrupt handling

  • Security

  • Providing a platform for software to run

  • Providing a user interface

  • Providing utilities

Resource Management

• Operating systems manage the computer's resources, including the CPU, memory, disk drives, and printers

• They allocate resources to specific tasks and ensure that they are used effectively

• e.g. when a user opens multiple applications simultaneously, the operating system decides:

  • How much memory to allocate to each application

  • When and for how long each gets to use the CPU

  • How to handle data being read from or written to the hard drive.

File Management

• Operating systems handle the storage, retrieval, and manipulation of data files

• When working with files, operating systems provide a GUI of the file system that allows a user to decide which directory a file should be saved in and what the file name will be

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

• E.g. 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

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

Providing a Platform for Software to Run

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

• e.g. 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 a User Interface

• Operating systems provide interaction in 2 ways: visually through a graphical user interface (GUI) or text-based through a command-line interface (CLI)

• Most modern PC operating systems provide both options, and a user will prefer one over the other depending on the task

• Mobile operating systems such as Android and iOS provide GUIs that are suitable for interaction through touch

• Ubuntu is an OS popular with software engineers because it provides a no-frills GUI and an efficient CLI

Providing Utilities

• Utility programs help with system maintenance and security

• Some utility programs include: file encryption, file compression, disk defragmentation, system backup, disk cleanup

• File encryption allows users to send files over networks securely

• File compression reduces the size of a file, which helps send large files over a network

• Disk defragmentation physically reorganises files on the hard disk so they can be found and accessed faster

• Disk cleanup scans the hard disk for duplicate and corrupt files and deletes them to create more space on the disk

• Backup software allows users to restore their system to a point in history