Operating Systems and Utility Software
What Is an Operating System?
Every computer needs software that manages its hardware and gives applications a platform to run on. An operating system (OS) sits between the hardware and the user-facing applications. Without an OS, every application would have to contain its own code for drawing text on screen, reading keyboard input and writing to disk — an enormous duplication of effort. The OS handles these common tasks so that applications can focus on their specific job.
The core of the OS is the kernel. The kernel runs continuously in the background, managing resources and mediating between hardware and software. It is the most privileged piece of software on the system — it can access all hardware directly, while applications must go through the kernel via system calls.
An operating system manages six key areas: CPU scheduling, memory management, backing store (file system) management, peripheral management, the user interface, and security. Each area has dedicated OS components.
CPU Management and Scheduling
A modern computer runs many processes at the same time — a web browser, a music player, background updates. The OS scheduler decides which process gets CPU time and for how long. Because the CPU switches between processes so rapidly, it creates the illusion of true simultaneous execution even on a single-core processor.
Two common scheduling algorithms are:
- Round-robin scheduling: each process gets a fixed slice of CPU time (a quantum) in turn. When a process’s quantum expires, the next process in the queue takes over, even if the first process hasn’t finished. This ensures fairness — no single process can monopolise the CPU.
- First-Come-First-Served (FCFS): processes run in the order they arrive in the queue. Simple to implement but unfair — a long process arriving first can block shorter ones for a long time.
Interrupts allow the OS to respond to urgent events without waiting for the current process to finish. When a key is pressed or a network packet arrives, the hardware sends an interrupt signal. The CPU pauses its current task, saves its state, handles the interrupt, then resumes what it was doing. Without interrupts, a computer could not respond to user input while running a program.
Memory Management
The OS controls how RAM is allocated between running programs. When more programs are open than RAM can hold, the OS uses paging — dividing memory into fixed-size blocks called pages. Inactive pages are moved to a reserved area of the backing store (virtual memory) — the secondary storage, such as a hard drive or an SSD. Using the backing store to extend RAM in this way is called virtual memory. When those pages are needed again, they are swapped back into RAM.
Virtual memory allows a computer to run programs that collectively need more RAM than is physically installed. The trade-off is speed: swapping pages to and from secondary storage is much slower than RAM access. If too much paging occurs, the system slows dramatically in a state called “thrashing.”
Paging divides RAM into fixed-size pages. Inactive pages are written to a reserved area of the backing store, which is the secondary storage. Using it this way is called virtual memory. Accessing the backing store is slower than RAM, so excessive paging causes the system to slow down.
Peripheral and File System Management
Peripherals — printers, keyboards, mice, external drives — each speak a different communication protocol. The OS uses device drivers: small software modules that translate between the OS’s generic commands and the specific signals each device understands. When you plug in a USB keyboard, the OS loads the relevant driver so that keystrokes reach the running application correctly.
The OS also manages the file system — how files are organised, named, stored and retrieved on backing storage. It maintains a directory structure (folders and subfolders), controls which users can read or write which files, and handles the physical reading and writing of data to the storage medium. Common file systems include NTFS (Windows), ext4 (Linux) and APFS (macOS).
User Interface and Security
The OS provides a user interface — the layer through which people interact with the computer. The two main types are the graphical user interface (GUI, which uses windows, icons and a pointer) and the command-line interface (CLI, which accepts typed commands). The OS also enforces security: user account authentication (logins and passwords), access permissions on files and folders, and software privilege levels that prevent applications from accessing each other’s memory.
Utility software is system software that maintains and optimises the computer. Unlike applications (which do user tasks like word processing), utilities work on the system itself. You need to know the following utilities and what each one does:
- Anti-virus software: scans files and processes for known malicious patterns (virus signatures) and removes or quarantines threats. Relies on regular signature updates.
- Backup software: makes copies of files to a separate location (external drive, cloud). Full backups copy everything; incremental backups copy only files changed since the last backup.
- Disk defragmenter: on traditional hard drives, files become fragmented — stored in non-contiguous sectors. A defragmenter reorganises files into contiguous blocks, reducing read-head movement and improving access speed. (Not needed on SSDs.)
- Disk compression: reduces the size of files on disk by encoding data more efficiently. Saves storage space at the cost of small processing overhead when reading and writing.
- Data recovery software: attempts to retrieve files that have been accidentally deleted or corrupted. Works because “deleting” a file usually only removes the directory entry — the data often remains until overwritten.
- File manager: provides a graphical or command-line interface to browse, copy, move, rename and delete files and folders. Windows Explorer and Finder are examples.
Beyond the six main utilities above, the specification also references:
- Archiver / compression utility: packages multiple files into a single compressed archive (e.g. ZIP, RAR). Useful for sending groups of files and reducing download sizes.
- Partition editor, disk formatter and disk checker: a partition editor divides a physical storage device into separate logical sections (partitions), each of which can hold a different file system or operating system. A disk formatter prepares a partition for use by writing a file system to it, which erases any data already stored there. A disk checker scans a drive for file system errors and bad sectors, then repairs what it can.
- Clipboard manager: extends the standard cut-and-paste clipboard to store a history of copied items, allowing users to paste earlier copied content.
- System profiler / diagnostic tool: reports detailed information about hardware (CPU type, RAM installed, GPU) and software (driver versions, installed applications). Used to diagnose compatibility and performance issues.
- Cryptographic utility: encrypts or decrypts files and communications using cryptographic algorithms, protecting sensitive data from unauthorised access.
- Revision control (version control): tracks changes to files over time, allowing earlier versions to be restored. Essential in software development (e.g. Git). Useful even for individual documents.
Students sometimes confuse the categories of software. The key distinction is purpose: the OS manages hardware resources and provides a platform; application software performs end-user tasks (word processing, gaming, browsing); utility software maintains the system. A word processor is not a utility; anti-virus software is not the OS. All three are software, but they serve distinct functions.
A second common confusion: utility software is part of system software (alongside the OS), but utility software is not the same as the OS. The OS kernel runs at the lowest level and starts first; utilities are higher-level tools that run on top of the OS and can be installed or removed independently.