Files, extensions and the operating system
A file is a saved piece of data with a name: a document, photo, song or program. Most names have two parts: name.extension.
.docx,.odt: text documents.pdf: a fixed page that looks the same everywhere.jpg,.png: images.mp3,.mp4: audio and video.xlsx,.csv: spreadsheets and data.zip: a compressed folder.exe,.app: programs (open only if you trust the source)
The operating system (Windows, macOS, Linux, Android) has a file manager (File Explorer, Finder, Files) to create, open, rename, copy, move, search and delete files. It keeps programs in their own folders (such as Program Files or Applications) and your work in user folders (Documents, Pictures, Downloads).
Folders, paths and drives
Folders make a tree
A folder (directory) holds files and other folders (subfolders). Together they form a tree: the drive or root at the base, folders as branches, files as leaves.
Strategies for organising
- By subject or project: School › Science › Lab reports.
- By date: Photos › 2026 › 2026-05 Trip.
- By type: Documents, Images, Videos.
- Keep it shallow (about 3–4 levels), avoid “New Folder (3)”, and keep an Archive folder for finished work.
Paths
A path is the full address of a file. Windows: D:\School\Science\lab-report_2026-09-12.docx (backslash \). macOS and Linux: /School/Science/lab-report_2026-09-12.docx (forward slash /).
Choosing a drive
- Local drive (internal SSD/hard disk): fast, but lost if the device breaks.
- External drive (USB pen drive, external disk): portable, good for backups, easy to lose.
- Network drive (school or office server): shared with a team, needs the network.
- Cloud storage: open from any device, needs internet and a strong password.
Size units: 1 KB ≈ 1,000 bytes, 1 MB ≈ 1,000 KB, 1 GB ≈ 1,000 MB, 1 TB ≈ 1,000 GB.
Naming files and everyday file operations
Naming rules
- Short and clear: say what is inside (
algebra-notes.pdf, notDoc1.pdf). - Use
-or_instead of spaces; avoid symbols like/ \ : * ? " < > |(the system forbids or misreads them). - Dates as YYYY-MM-DD (2026-09-12) so files sort in time order.
- Versions as v1, v2, not “final FINAL”.
Operations
- Copy: makes a second file; the original stays.
- Move (cut and paste): the same file goes to a new place.
- Rename: change the name, keep the extension.
- Delete: goes to the Recycle Bin / Trash first, so you can restore it until the bin is emptied.
- Search: find files by name, type or date.
- Compress (zip): packs files into one smaller file, good for emailing and archiving.
Backup, archiving and protecting files from malware
Backup
A backup is an extra copy in another place. Use the 3-2-1 rule: 3 copies of important files, on 2 kinds of storage (for example laptop + external drive), with 1 copy off-site (cloud or another building).
- Full backup: copies everything. Incremental backup: copies only what changed since the last backup, so it is faster.
- Back up on a schedule (daily or weekly) and test that you can restore a file.
Archiving
An archive stores finished work you rarely need (last year’s projects). Zip it, label it with the year, and keep it on cheaper storage. Archive ≠ backup: an archive may be the only copy, so back it up too.
Safety from malware
Malware is harmful software: viruses, worms, spyware and ransomware (locks your files and demands money).
- Keep the operating system and antivirus updated.
- Do not open unknown attachments or download from untrusted sites.
- Use strong passwords and two-step login for cloud accounts.
- Scan pen drives before opening files.
- An offline backup is the best cure for ransomware.
Key formulas and definitions
- File name = name + . + extension (e.g. notes.pdf)
- Path = drive + folders + file name (D:\School\Science\notes.pdf)
- 3-2-1 backup: 3 copies, 2 kinds of storage, 1 off-site
- 1 GB ≈ 1,000 MB; 1 MB ≈ 1,000 KB
- Copy = two files; Move = one file in a new place
- Date format for names: YYYY-MM-DD
Worked examples
1. Write the Windows path of the file trip_2026-05.jpg kept in the Photos folder on drive D.
D:\Photos\trip_2026-05.jpg. On macOS/Linux style it would be /Photos/trip_2026-05.jpg.
2. A class has 40 photos of 5 MB each. Will they fit on a 256 MB pen drive?
Total = 40 × 5 = 200 MB. 200 MB is less than 256 MB, so yes, with 56 MB to spare.
3. Rename these badly named files: “final FINAL 2.docx” (history essay) and “IMG001.jpg” (science fair, 3 March 2026).
history-essay_v2.docx and science-fair_2026-03-03.jpg: clear topic, no spaces, version or date in a sortable form.
Common mistakes
- Saving everything on the desktop or in Downloads. Files get lost; use a folder plan.
- Thinking a deleted file is gone at once. It usually waits in the Recycle Bin until the bin is emptied.
- Keeping the only copy on one device. If it breaks or is stolen, the work is lost; follow 3-2-1.
- Changing the extension to “convert” a file (photo.jpg → photo.pdf). The data does not change; the file may stop opening. Use Save As or Export.