What you'll learn
Systems software is the software that runs and manages a computer rather than performing a task for the user. In OCR GCSE Computer Science (J277, section 1.5) you need to know the purpose and functions of the operating system — user interface, memory management and multitasking, peripheral management and drivers, user management and file management — and the purpose of utility software, including encryption software, defragmentation and data compression. This guide explains each function, why it is needed, and how it appears in exam questions.
Questions in this area are often short (state a function, describe what it involves), but there are also explanation questions such as "explain why defragmentation improves performance" or "describe how the operating system manages memory". Being able to give a specific, accurate description of each function is the key to full marks.
Key terms and definitions
Systems software — Software that manages the computer's hardware and provides a platform for applications, including the operating system and utilities.
Operating system (OS) — Systems software that manages hardware and software resources and provides a user interface.
User interface — The means by which a user interacts with the computer, such as a GUI or command-line interface.
Memory management — The OS function that allocates RAM to programs and moves data between RAM and virtual memory.
Multitasking — Running more than one program apparently at the same time, by sharing processor time.
Peripheral — An input, output or storage device connected to the computer.
Device driver — Software that allows the operating system to communicate with a specific hardware device.
User management — Creating and controlling user accounts, passwords and access rights.
File management — Organising files into folders and controlling how they are named, saved, moved, copied and deleted.
Utility software — Software that helps to maintain, configure or protect the computer.
Encryption software — Utility software that scrambles data so it cannot be understood without a key.
Defragmentation — Reorganising files on a hard disk so that their parts are stored together.
Compression — Reducing the size of a file, either lossily or losslessly.
Core concepts
Why an operating system is needed
Without an operating system, every program would need to include code to control every piece of hardware it used — the screen, the keyboard, the disk, the printer — and programs could not safely run side by side. The OS sits between the hardware and the applications, managing resources and offering a consistent interface. Examples include Windows, macOS, Linux, Android and iOS.
Providing a user interface
The OS provides a way for users to interact with the computer:
- A graphical user interface (GUI) uses windows, icons, menus and pointers. It is intuitive and easy for beginners, but uses more memory and processing power.
- A command-line interface requires typed commands. It is efficient for experts, allows tasks to be automated with scripts and uses few resources, but is harder to learn.
- Touch interfaces use gestures on a touchscreen, while voice interfaces respond to spoken commands.
The user interface also handles things like displaying error messages, prompting the user and showing the status of tasks.
Memory management and multitasking
When a program runs, it must be loaded into RAM. The OS:
- allocates areas of RAM to each program and its data;
- keeps programs separate, so one program cannot overwrite another's memory, which would cause crashes or security problems;
- frees memory when a program closes so it can be reused;
- moves data to and from virtual memory when RAM is full, swapping out data not currently in use.
Multitasking lets several programs appear to run at once. The CPU can only process one instruction per core at a time, so the OS shares processor time between programs, switching between them so quickly that they appear simultaneous. The OS decides which program gets processor time next (scheduling), based on priorities.
Peripheral management and drivers
The OS manages communication with peripherals such as keyboards, mice, printers, monitors and storage devices. It handles input from them and sends output to them, and manages queues — for example, a print queue holding several documents until the printer is ready.
Each device works differently, so the OS uses device drivers: small programs that translate the OS's general instructions into the specific commands understood by that device. When a new device is connected, the correct driver must be installed. Drivers are often updated to fix problems or add features. Because of drivers, applications do not need to know details of each printer model; they simply send a print request to the OS.
User management
On computers with several users, the OS:
- creates and deletes user accounts;
- manages logins, usually with usernames and passwords (and sometimes biometrics);
- sets access rights so users can only open, edit or delete files they are permitted to;
- may keep a log of user activity;
- applies settings for each user, such as their desktop and preferences.
This protects privacy and security, especially on shared or networked computers such as those in schools.
File management
The OS organises data stored on secondary storage. It allows users to:
- create, name and rename files and folders;
- save, open, move, copy and delete files;
- organise files in a hierarchical folder structure;
- search for files;
- set permissions on files, such as read-only.
It also keeps track of where each file is physically stored on the device.
Utility software
Utility programs perform specific maintenance and protection tasks. You must know three in particular.
Encryption software. Encrypts data so it is unreadable without the correct key. It can encrypt individual files, folders, whole drives or data being sent across networks. If a laptop or USB drive is lost or stolen, encrypted data cannot be read by the finder. The key must be kept safe; if it is lost, the data cannot be recovered.
Defragmentation software. On a hard disk drive, when files are saved, deleted and changed over time, parts of a single file can become scattered across different areas of the disk — this is fragmentation. Reading a fragmented file requires the read/write head to move to many places, which slows access. Defragmentation reorganises the disk so each file's parts are stored contiguously (next to each other), and groups free space together. This reduces head movement and makes files faster to read and write.
Defragmentation is not needed on SSDs: they have no moving parts, so the location of data does not affect access speed, and the extra writing involved would wear out flash memory unnecessarily.
Data compression software. Reduces the size of files so they take up less storage space and can be transmitted more quickly, for example when emailing or uploading. Lossless compression allows the original file to be perfectly reconstructed (needed for text and program files). Lossy compression permanently removes some data that is less noticeable, giving much smaller files, and is used for images, audio and video.
Other utilities include backup software, anti-malware software, disk clean-up tools and system monitoring tools.
Other utility software
As well as the three utilities named in the specification, you may meet others in scenarios:
- Backup software copies files so they can be restored after loss. A full backup copies everything; an incremental backup copies only the files changed since the last backup, which is quicker and uses less space but means several backups are needed to restore everything. Backups can be scheduled automatically.
- Anti-malware software scans for, quarantines and removes viruses, spyware and other malware, and should be updated regularly.
- Disk clean-up tools remove temporary and unnecessary files to free space.
- System monitoring tools show how much processor, memory and storage is being used, helping identify problems.
All utilities share one purpose: they maintain, protect or optimise the computer rather than performing an end-user task such as writing a document.
How the functions work together
When you open a document in a word processor, several OS functions cooperate: the user interface registers your click; file management locates the file on secondary storage; memory management allocates RAM and loads the file; multitasking shares processor time with other programs; and if you print, peripheral management sends the job to the print queue using the printer's driver. Describing such a chain is a good way to show you understand the OS as a whole.
Worked examples
Example 1: Memory management
Describe how the operating system manages memory. (3 marks)
Answer: It allocates areas of RAM to each program that is running (1). It keeps the programs' memory separate so they do not overwrite each other's data (1). When RAM is full, it moves data not currently in use into virtual memory on secondary storage (1).
Example 2: Defragmentation
Explain why defragmenting a hard disk drive can improve performance. (3 marks)
Answer: Over time, parts of files become stored in different places on the disk (fragmented) (1). Reading a fragmented file requires the read/write head to move between many locations, which takes time (1). Defragmentation moves the parts of each file so they are stored together, so files can be read more quickly (1).
Example 3: Device drivers
A user plugs a new printer into a computer. Explain why a device driver is needed. (2 marks)
Answer: The operating system needs to communicate with the printer (1), and the driver translates the OS's general instructions into commands that the specific printer model understands (1).
Example 4: Choosing a utility
A company's sales staff carry laptops containing customer data. Which utility software would protect the data if a laptop is stolen? Explain.
Answer: Encryption software. If the drive is encrypted, the thief cannot read the customer data without the decryption key, so it remains protected even though the laptop is lost.
Common mistakes and how to avoid them
- Listing OS functions without describing them. "Memory management" alone often earns only one mark; describe what it involves.
- Recommending defragmentation for SSDs. It only benefits hard disks and can shorten SSD life.
- Confusing the OS with applications. Word processors and browsers are application software.
- Saying compression always loses quality. Lossless compression keeps all data.
- Saying drivers are hardware. They are software.
Exam technique for "Systems Software"
- Learn the five OS functions — user interface, memory management/multitasking, peripheral management and drivers, user management, file management — with two facts about each.
- For "explain" questions, give the problem, the action the software takes and the result.
- Use the term contiguous when describing defragmentation and access rights when describing user management.
Quick revision summary
- The OS manages hardware and software and provides a user interface.
- User interface: GUI, command line, touch, voice.
- Memory management: allocates RAM, keeps programs separate, uses virtual memory; multitasking shares CPU time.
- Peripheral management: controls devices and queues using drivers.
- User management: accounts, logins, access rights.
- File management: folders, naming, saving, moving, deleting, permissions.
- Utilities: encryption (protects data), defragmentation (HDDs only, faster access), compression (smaller files; lossy or lossless).