Official operating system downloads
Every entry below is published by the vendor that makes the software — Microsoft for Windows, Apple for macOS, Canonical and the Fedora and Debian projects for Linux. The hostname is printed next to each link so you can see where it goes before you click.
Windows
Microsoft publishes the ISO, the media creation tool and the upgrade assistant from one page. Which of the three you want depends on whether you are upgrading in place or building install media.
The only place Windows 11 comes from. The page offers the Installation Assistant for in-place upgrades, the Media Creation Tool for building a USB stick, and the direct ISO download for everything else.
Still available for machines that cannot meet the Windows 11 requirements, or for software that will not run on it. Support ended on 14 October 2025, so treat this as a compatibility fallback rather than a destination.
A full, genuine Windows 11 Enterprise image, free from Microsoft, licensed for 90 days of evaluation. The legitimate option for a test machine, a lab, or a VM you need for a month.
Pre-release Windows builds, from Microsoft, for people who want to test upcoming versions. Opt in and the builds arrive through Windows Update; no ISO hunting required.
Microsoft's own instructions for the Media Creation Tool, including what the tool needs and what it does at each step. Read this instead of a tutorial blog if you want the current wording of every prompt.
Known issues and rollout status for every supported Windows release. Check here before reinstalling: if Microsoft has already acknowledged your symptom, reinstalling will not fix it and will cost you an afternoon.
The actual hardware requirements: TPM 2.0, UEFI Secure Boot, 4 GB RAM, 64 GB storage, a supported CPU. Worth two minutes before you download 5.5 GB.
macOS
Apple does not distribute macOS as a downloadable ISO from a public page. The installers come through the App Store and through its support pages — the links below are those pages, not third-party copies of the result.
Apple's hub for every route to a macOS installer: Software Update, macOS Recovery, Terminal, and the App Store links for the current release and older ones. Start here rather than at a downloads directory.
The createinstallmedia walkthrough, including the exact command for every release back to El Capitan. The command is copied from Apple rather than retyped, which matters: one wrong character produces an unbootable drive.
The canonical answer to “will I lose my files?” Apple states it directly: reinstalling macOS does not remove your apps or personal data. Includes which macOS version you get depending on how you entered Recovery.
How to reach Recovery on both Apple silicon and Intel Macs, and what to do when it will not start. The key combinations differ by chip, and getting this wrong is the most common stumbling block.
Apple's own developer resource centre, which hosts full macOS installers and betas alongside Xcode. Requires a developer account, and carries beta software with the usual caveats.
Where the App Store links on Apple's macOS page lead. The installer downloads as a normal App Store purchase, which is why it appears without a visible ISO.
USB writing tools
These are not operating systems. They are the upstream projects for writing an image to a USB drive, listed because the guides refer to them and because a version downloaded from a bundle site is not the version the project publishes.
The standard tool for writing a Windows ISO to a USB stick. Small, open source, no installer, and it lets you set the partition scheme and target system explicitly — which is what you need when a stick refuses to boot.
Installs a bootloader to a USB drive once, after which you copy ISO files onto it as ordinary files and choose between them at boot. Worth the setup if you reinstall machines regularly or keep several operating systems on one stick.
A cross-platform image writer with the simplest possible interface. Handy when you are preparing a Windows or Linux stick from a Mac, where Rufus is not an option.
Linux
Included for completeness. Most people reinstalling a laptop are choosing between Windows and macOS, but these are the official pages if you are not.
Verifying a download
A file arriving from the vendor's own server is your first and strongest protection. If you want to go further, these are the checks that are actually meaningful.
Check the digital signature on Windows media
A genuine Microsoft ISO can be inspected from PowerShell. Mount the image and check its signature:
Get-AuthenticodeSignature D:\setup.exe | Format-List
Look for a status of Valid and a signer of
Microsoft Corporation. A signed setup.exe
means the installation engine is genuine. This does not prove the whole image
is byte-identical to Microsoft's, but a forged signature is not something you
will encounter from a random repack.
Check a macOS installer
Apple installers are signed and notarised. Confirm the app you downloaded is the one Apple shipped:
pkgutil --check-signature "/Applications/Install macOS Sequoia.app"
You want the signature to chain to Apple Inc. Any other result means the installer is not Apple's.
Check disk integrity before you reinstall
Not a download check, but the other reason installs fail. On macOS, run
First Aid from Disk Utility before erasing; on Windows, run
chkdsk on the system drive while the old
installation still works. Finding out the drive is failing after you have
wiped it is a bad trade.
What not to do
Do not download a “verified” image from a file host whose checksum list was published by the same uploader. Do not use a downloader that fetches from several mirrors automatically. And do not install an activation tool of any kind — see the activation section of the Windows guide for what that costs.