System Software

OS purpose: Managing resources (peripherals, processes, memory, backing store)

The operating system (OS) is the most important piece of system software on a computer. It acts as an intermediary between the user and the hardware, managing all of the computer’s resources so that application software can run smoothly.

The OS manages four key types of resource:

Peripheral Management

• The OS controls all input and output devices (peripherals) connected to the computer
• It uses device drivers — small programs that translate general OS commands into specific instructions for each device
• When a peripheral needs attention (e.g. a key is pressed), it sends an interrupt to the CPU, and the OS handles it
• The OS maintains a queue of print jobs and other I/O requests, sending them to the correct device in order

Process Management

• A process is a program that is currently being executed
• The OS allocates CPU time to each process so that multiple programs appear to run simultaneously
• On a single-core processor, the OS uses time slicing — rapidly switching between processes so each gets a share of the CPU
• The OS decides the order using scheduling algorithms, which consider priority, waiting time, and fairness
• It also handles starting, pausing, resuming and terminating processes

Memory Management

• The OS allocates RAM to each running process and keeps track of which memory locations are in use
• When a program is opened, the OS loads it into an available section of RAM
• When a program closes, the OS frees that memory for other processes
• If RAM becomes full, the OS may use virtual memory — a section of the hard drive that temporarily acts as extra RAM
• Virtual memory is much slower than RAM, so heavy use causes the system to slow down (known as disk thrashing)

Backing Store Management

• The OS manages how files are stored on secondary storage (hard drives, SSDs)
• It uses a file system (e.g. NTFS, FAT32, ext4) to organise files into folders and keep track of where each file’s data is physically located on the disk
• The OS handles file operations: creating, reading, writing, deleting, copying and moving files
• It manages access rights — controlling which users can read, write or execute particular files
• The OS also keeps a directory structure so the user can navigate and find files easily

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OS purpose: Providing a user interface

The OS provides a user interface that allows people to interact with the computer. Different types of interface suit different users and tasks.

Types of User Interface

Interface Type	Description	Advantages	Disadvantages
GUI (Graphical User Interface)	Uses windows, icons, menus and pointers (WIMP)	Intuitive, easy to learn, visually clear	Uses more system resources, slower for experts
CLI (Command Line Interface)	User types text commands	Powerful, fast for experts, uses fewer resources	Steep learning curve, must memorise commands
Menu-driven	Presents numbered or listed options to choose from	Simple, no commands to learn	Limited options, can be slow to navigate
Natural language	User speaks or types in everyday language	Very accessible, no training needed	Can misinterpret input, limited functionality
Touch-sensitive	User taps, swipes and pinches directly on a touchscreen	Intuitive, no extra peripherals needed, portable	Less precise than a mouse, prone to fingerprints, limited for complex tasks
Voice-driven	User speaks commands interpreted by voice recognition	Hands-free, accessible for users with disabilities	Affected by background noise, accents can cause errors, limited command set

GUI (Graphical User Interface)

• The most common interface on desktop and laptop computers
• Users interact by clicking icons, dragging files, and selecting from menus
• Uses a WIMP system — Windows, Icons, Menus, Pointers
• Allows multitasking by showing multiple windows on screen at once
• Examples: Windows desktop, macOS Finder, smartphone home screens

CLI (Command Line Interface)

• The user types precise text commands to perform operations
• Provides direct control over the system, with no visual overhead
• Commonly used by system administrators and programmers for tasks such as managing servers, automating scripts, and navigating file systems
• Commands can be combined and saved as scripts to automate repetitive tasks
• Examples: Windows Command Prompt, PowerShell, Linux Terminal

Touch-Sensitive Interface

• The user interacts directly with the screen by tapping, swiping, pinching and dragging
• Common on smartphones, tablets, ATMs, self-service checkouts and information kiosks
• Very intuitive — even young children can use it with no training
• Less suitable for tasks requiring precise input (e.g. detailed graphic design) or large amounts of text
• Screens can become dirty and difficult to read due to fingerprints

Voice-Driven Interface

• The user speaks commands which are interpreted by voice recognition software
• Used in smart speakers (Alexa, Google Home), virtual assistants (Siri, Cortana), and accessibility tools
• Allows hands-free operation — useful while driving, cooking, or for users with physical disabilities
• Accuracy can be reduced by background noise, strong accents, or unusual vocabulary
• Privacy concerns — the device may be always listening to detect the wake word

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Utility software: Purpose and functionality

Utility software is a type of system software designed to help maintain, optimise and protect the computer system. Utilities perform specific housekeeping tasks that keep the system running efficiently.

Common Utility Programs

Utility	Purpose	How it Works
Antivirus	Protects against malware	Scans files and programs against a database of known virus signatures; quarantines or deletes threats
Disk defragmenter	Improves HDD performance	Rearranges fragmented file data so that each file is stored in contiguous blocks, reducing read/write times
Backup software	Protects against data loss	Creates copies of files that can be restored if the originals are lost, corrupted or accidentally deleted
File compression	Reduces file size	Uses algorithms to reduce the number of bits needed to store a file, saving space and speeding up transfers
Encryption software	Protects data security	Scrambles data using an algorithm and a key so it cannot be read without the correct decryption key
File manager	Organises files and folders	Allows users to browse, move, copy, rename and delete files within the file system
Firewall	Prevents unauthorised network access	Monitors incoming and outgoing traffic and blocks connections that violate security rules
Disk partitioner	Divides a drive into logical sections	Splits a physical hard drive into separate partitions, each of which can act as an independent drive
Disk checker	Detects and repairs file system errors	Scans the disk for bad sectors, corrupted files and file system inconsistencies and attempts to repair them
Disk formatter	Prepares a disk for use	Erases all data and sets up a new file system (e.g. NTFS, FAT32) so the OS can read and write to the disk
Disk compression	Compresses entire drives to save space	Automatically compresses and decompresses files as they are written to and read from the disk
System profiler	Displays system information	Shows details about hardware components, installed software, OS version and resource usage
Data recovery	Recovers lost or deleted files	Scans storage media for remnants of deleted files and attempts to restore them
Clipboard manager	Extends clipboard functionality	Stores a history of copied items so the user can paste from previous clipboard entries, not just the most recent
Version control	Tracks changes to files over time	Records every change made to a set of files, allowing users to revert to previous versions and compare changes
Archiver	Combines and compresses multiple files	Packages multiple files and folders into a single archive file (e.g. .zip, .tar) for easier storage and transfer

Antivirus Software

• Runs real-time scans in the background to check files as they are opened or downloaded
• Performs full system scans on a schedule to check all stored files
• Compares files against a database of known virus signatures (patterns of code)
• Uses heuristic analysis to detect suspicious behaviour from previously unknown threats
• Must be regularly updated so that the signature database includes the latest threats

Disk Defragmentation

• Over time, files are saved in non-contiguous (fragmented) blocks across a hard drive
• The read/write head must jump between scattered blocks, slowing down file access
• Defragmentation rearranges data so that files are stored in adjacent blocks
• This reduces seek time and improves performance
• Only needed for HDDs — SSDs should not be defragmented as it wears out the flash memory unnecessarily

Backup Software

• Creates copies of data that can be used for recovery after data loss
• Full backup: copies all selected files — thorough but time-consuming and storage-heavy
• Incremental backup: only copies files that have changed since the last backup — faster and uses less space
• Good practice is to follow the 3-2-1 rule: 3 copies of data, on 2 different types of media, with 1 stored off-site

File Compression

• Lossy compression permanently removes some data to achieve smaller file sizes (e.g. JPEG images, MP3 audio) — the original cannot be perfectly restored
• Lossless compression reduces file size without any loss of data (e.g. ZIP, PNG) — the original can be perfectly restored
• Compressed files take up less storage space and can be transferred faster over a network

Firewall

• Monitors all incoming and outgoing network traffic and checks it against a set of security rules
• Blocks unauthorised access — prevents external users or programs from connecting to the computer without permission
• Can be software-based (a program installed on the computer) or hardware-based (a dedicated device between the network and the internet)
• Protects against hackers and malicious connections by filtering traffic based on IP addresses, port numbers and protocols
• Works alongside antivirus software to provide a layered approach to security

Disk Partitioner

• Divides a single physical hard drive into separate logical sections called partitions
• Each partition can act as a separate drive, with its own drive letter and file system
• Useful for running multiple operating systems on the same machine (e.g. Windows on one partition, Linux on another)
• Allows users to separate OS files from user data, making it easier to reinstall the operating system without losing personal files
• Can resize, create or delete partitions as needed

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Hierarchical File Structure

The OS organises files into a hierarchical (tree) structure of folders (directories) and subfolders. This makes it possible to locate and manage files efficiently.

Key Concepts

• Root directory — the top-level folder on a drive (e.g. C:\ on Windows, / on Linux/macOS)
• Directory (folder) — a container that holds files and other subdirectories
• Subdirectory — a folder inside another folder
• File path — the route from the root to a specific file, e.g. C:\Users\Alex\Documents\homework.docx

Example Structure

C:\
├── Program Files
│   ├── Browser
│   └── Office
├── Users
│   └── Alex
│       ├── Documents
│       │   └── homework.docx
│       ├── Pictures
│       └── Music
└── Windows
    └── System32

File Attributes

Every file stored by the OS has attributes — properties that describe and control the file.

Attribute	Description
Filename	The name given to the file by the user
Extension	Indicates the file type (e.g. .docx, .jpg, .py)
File size	The amount of storage the file occupies (in bytes, KB, MB, etc.)
Date created	When the file was first created
Date modified	When the file was last changed
Read-only	If set, the file can be viewed but not edited or deleted
Hidden	If set, the file is not displayed in normal folder views
System	Marks a file as part of the OS — should not be modified by the user
Archive	Indicates whether the file has changed since the last backup
Permissions	Controls which users can read, write or execute the file