Operating Systems (OCR A Level Computer Science)
Revision Note
Written by: Callum Davies
Reviewed by: James Woodhouse
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
Worked Example
Operating systems usually come with utility software pre-installed.
Give two examples of utility software, explaining the purpose of both.
[4]
How to answer this question:
You need to name two different examples of utility software and the purpose of each:
Backup software: creates system snapshots and will restore them on demand
Disk defragmentation: reorganises the hard disk so that files are better organised
File compression: reduces file size to consume less hard disk space or for faster transfer over a network
Disk cleanup: finds and removes duplicate or corrupted files, freeing up hard disk space
File encryption: Encodes files before transfer, will decode files that have been received
For each utility, include why it's helpful in your answer
Answer:
Example answer that gets full marks:
Disk defragmentation is a utility that will better organise files on the hard disk so that the operating system can access them more efficiently. Better organised files will lead to a smoother operation of the system.
File encryption software will encode the contents of a file into a non-readable format. If files containing sensitive data are lost or stolen, the contents will be protected from misuse.
Acceptable answers you could have given instead:
Disk cleanup will scan the hard disk for duplicate files and remove them.
Backup software will allow users to restore a system to a previous point.
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