Operating Systems, Software and File Systems Explained (Tech+)
What you’ll know
What the operating system does for you, how the main ones differ, why a USB stick formatted one way won’t take a 5 GB file, what file extensions mean, and how updates and licences work.
Why it matters. Half of all “it won’t open” and “it won’t copy” problems come down to the operating system, the file system or a missing app. These basics make the fix obvious.
What the operating system does
- Runs the hardware: talks to the CPU, memory, drives and devices through drivers.
- Runs your apps and shares the computer’s resources between them.
- Manages files and folders on the drive.
- Controls who can log in and what each account is allowed to do.
The main operating systems
| OS | Found on | Good to know |
|---|---|---|
| Windows | Most work and home PCs | Most software and games; the usual target for malware too. |
| macOS | Apple Macs | Built on Unix, so its Terminal works much like Linux. |
| Linux (Ubuntu, Debian, Fedora…) | Servers, cloud, security tools, Raspberry Pi | Free and open source; runs most of the internet. |
| Android | Most phones and many tablets | Built on the Linux kernel. |
| iOS / iPadOS | iPhone and iPad | Apps come from Apple’s App Store only. |
| ChromeOS | Chromebooks | Mostly web apps; popular in schools. |
File systems: why the USB stick says “file too large”
| File system | Used by | Biggest single file |
|---|---|---|
| NTFS | Windows system drives | Effectively unlimited for home use; also stores permissions. |
| FAT32 | Old USB sticks, cameras | 4 GB, which is why a 5 GB movie won’t copy. |
| exFAT | Modern USB sticks and SD cards | Effectively unlimited, and works on Windows and Mac. |
| ext4 | Most Linux systems | Linux’s default. |
| APFS | Macs, iPhones | Apple’s default. |
Reformatting a stick from FAT32 to exFAT fixes the 4 GB limit, but formatting erases everything on it, so copy the files off first.
File extensions
The letters after the last dot tell the OS which app opens a file: .docx (Word), .pdf, .jpg, .mp4, .zip. Programs end in .exe or .msi on Windows. Windows hides extensions by default, which is how invoice.pdf.exe fools people. Turn them on in File Explorer: View > Show > File name extensions.
Updates and licences
- Updates fix security holes as well as bugs. Most attacks on home PCs use flaws that already have a fix, so turn on automatic updates.
- Open source: the code is public and usually free to use (Linux, Firefox, LibreOffice).
- Proprietary: owned by a company; you buy a licence or a subscription (Microsoft 365, Adobe).
- Freeware costs nothing but isn’t necessarily open; shareware is a trial you’re expected to pay for.
A file called cute_kittens.jpg.exe is not kittens. I checked. Twice. Show your file extensions. — Nyx
Try it: which OS and file system do you have?
PS> (Get-CimInstance Win32_OperatingSystem).Caption PS> Get-Volume | Select-Object DriveLetter,FileSystem,Size
The first line prints your Windows edition. The second lists each drive with its file system (NTFS, FAT32, exFAT) and size in bytes. Plug in a USB stick first to see how it’s formatted.
$ grep PRETTY_NAME /etc/os-release $ df -hT /
/etc/os-release names your Linux distribution; df -hT shows the file system type (usually ext4) and how full the drive is.
Where this fits
This is part of the free CompTIA Tech+ roadmap: computer basics in the order the exam teaches them.
NextStrong passwords and passphrases→
Go deeper
- Computer hardware explained — the parts the OS is managing
- How to open Command Prompt and PowerShell — for the commands above
- Read email headers and report phishing — where fake attachments usually arrive
Explainer, written by StashGrid with AI help and checked against the CompTIA Tech+ (FC0-U71) exam objectives before publishing. Every command was run on a Windows 11 PC and in Ubuntu 24.04 (WSL) on 30 Oct 2026. StashGrid isn’t affiliated with CompTIA. Spotted an error? Tell us.