What Is a File and How Does File Management Work? KS3 Computing

A file is a named collection of related data stored persistently on a storage device. Every document, photo, program, and song on your computer is a file. At KS3, understanding how files are structured, organised into directories, identified by extensions, and managed efficiently is a practical part of the curriculum linked to hardware and networks.

What is a file?

A file is a discrete, named unit of data stored on a storage device such as a hard drive, SSD, or USB stick. The operating system treats a file as a single entity with a name, a type, a size, and metadata (such as the date created and date modified).

At the hardware level, a file is simply a sequence of bits — 0s and 1s — stored on a physical medium. The operating system's file system (such as NTFS on Windows, APFS on macOS, or ext4 on Linux) keeps track of where on the storage device each file's data begins and ends, what the file is called, and when it was last modified.

Without a file system, the storage device would just be a long stream of undifferentiated bits, with no way to identify which bits belong to which file.

What is a file extension and what does it tell you?

A file extension is the suffix at the end of a filename, separated by a full stop. It indicates the file's type and therefore which programs can open it.

Extension | File type | Typical application
.txt | Plain text | Notepad, any text editor
.docx | Word processing document | Microsoft Word
.pdf | Portable Document Format | Adobe Reader, browsers
.jpg / .jpeg | JPEG image | Photo viewers, web browsers
.png | PNG image | Photo viewers, web browsers
.mp3 | MPEG audio | Music players
.mp4 | MPEG-4 video | Video players
.py | Python source code | Python IDE, text editor
.html | HTML webpage | Web browsers
.zip | Compressed archive | File managers, WinZip

The operating system uses the extension to decide which program to launch when you double-click a file. Renaming .jpg to .txt does not convert the file — it just misleads the OS about the format. The actual binary contents of the file do not change.

What is a directory and how does a file system organise files?

A directory (also called a folder) is a container for organising files. Directories can contain other directories — these are called subdirectories — creating a hierarchical tree structure.

C:\
├── Users\
│ └── Aisha\
│ ├── Documents\
│ │ ├── coursework.docx
│ │ └── notes.txt
│ ├── Pictures\
│ │ └── holiday.jpg
│ └── Desktop\
│ └── shortcut.lnk
├── Windows\
└── Program Files\

Every file has a file path — the sequence of directories from the root of the file system to the file itself. File paths use a separator character: backslash \ on Windows, forward slash / on Linux and macOS:

Windows: C:\Users\Aisha\Documents\coursework.docx

Linux/macOS: /home/aisha/Documents/coursework.docx

An absolute path begins at the root of the file system (like a full postal address). A relative path begins at the current working directory (like "turn left at the corner" rather than giving the full address).

What is file compression?

File compression reduces the size of a file (or a collection of files) by encoding the data more efficiently, removing redundancy. A compressed file takes up less storage space and transfers more quickly over a network.

There are two types of compression:

Lossless compression — all original data is perfectly preserved. The decompressed file is bit-for-bit identical to the original. Used for: text files, program code, spreadsheets, and ZIP archives.

Lossy compression — some data is permanently removed to achieve higher compression ratios. The decompressed result is an approximation of the original, not identical. Used for: JPEG images, MP3 audio, MP4 video — where small reductions in quality are imperceptible or acceptable.

Type | Data loss | Typical ratio | Examples
Lossless | None | 2:1 to 10:1 | ZIP, PNG, FLAC
Lossy | Some | 10:1 to 100:1 | JPEG, MP3, MP4

A high-resolution photograph might be 10 MB as a raw file. Saved as a JPEG with moderate compression it might be 500 KB — a 20:1 reduction — with only minor, barely visible loss of quality.

How should you manage files effectively?

Good file management is a practical skill with direct relevance to every piece of coursework you submit. Key principles:

Use descriptive, consistent names — physics_homework_2026-07-02.docx rather than doc1.docx. Include the date in ISO format (YYYY-MM-DD) so files sort chronologically.

Use a logical folder hierarchy — organise by subject, then by topic, then by year. Avoid storing everything in one folder or on the desktop.

Back up regularly — follow the 3-2-1 rule: 3 copies of data, on 2 different media types, with 1 copy off-site (e.g. cloud storage).

Delete files you no longer need — storage is not infinite, and unnecessary files slow down backups and searches.

Use version control for important work — saving files with version numbers (e.g. essay_v1.docx, essay_v2.docx) protects against accidental overwrites.

The DfE computing programme of study requires students to understand how data is stored and managed (gov.uk/government/publications/national-curriculum-in-england-computing-programmes-of-study). File systems and management are foundational knowledge for operating systems, networking (file servers, cloud storage), and data security topics.

Frequently asked questions

What is a file in computing for KS3?

A file is a named collection of related data stored as a single unit on a storage device. It could contain text, images, audio, video, program code, or any other kind of digital data. The operating system keeps track of files using a file system, which records each file's name, type, size, and location on the storage medium.

What is a file extension and why is it important?

A file extension is the suffix after the final full stop in a filename (e.g. .txt, .jpg, .mp3). It identifies the file's format and tells the operating system which application to use to open it. Without the extension, the OS does not know how to interpret the file's contents. Changing the extension does not change the underlying data — it only changes how the OS tries to open the file.

What is the difference between lossless and lossy compression?

Lossless compression reduces file size without losing any data — the decompressed file is identical to the original. It is used where accuracy is essential: text documents, program files, and PNG images. Lossy compression achieves much higher compression ratios by permanently discarding some data, producing an approximation of the original. It is used where small quality reductions are acceptable: JPEG images, MP3 audio, and streaming video.

What is a file path?

A file path is the address that specifies the exact location of a file within a file system's directory structure. An absolute path starts from the root of the file system (e.g. C:\Users\Aisha\Documents\notes.txt on Windows). A relative path starts from the current directory (e.g. if you are already in C:\Users\Aisha\, the relative path to the same file is Documents\notes.txt).

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