turing-os-1.3.14-amd64.iso — 5.6 GB. It is a disk image: you write it to a USB stick and start the computer from that stick.

You need a USB stick of 8 GB or more. Everything already on it will be erased. Copying the file onto the stick does not work — the image has to be written to it as a whole disk, which is what the tool below does.

1. Install and open balenaEtcher. It is free, and works the same on Windows, macOS and Linux.
2. Flash from file — choose the image you have just downloaded.
3. Select target — choose your USB stick. Check the size; it is the one thing here that is easy to get wrong.
4. Flash, then wait. Around ten minutes.

On Windows you can use Rufus instead, with its default settings. If Windows offers to format the stick when you plug it back in, say no — the stick is fine, Windows simply cannot read it.

Leave the stick plugged in and restart. As the machine starts, press the boot menu key repeatedly — F9 on an HP, F12 on most others — and pick the stick from the list. The desktop runs from the stick, so you can look around before anything is written to the computer. The installer asks for your activation code once.

The full guide has the boot key for every make, what the installer does to your disk, and what happens afterwards.

Haven't bought it yet? The licence is £102, once — the image will sit there until you have it. Lost your code? Ask for it again; it is emailed to the address you bought with. Anything else, info@turing.london.