Bootable USB drives, and making one before you need it

A bootable USB drive lets you start a computer from something other than its own hard drive. That sounds niche until the day the machine will not start, at which point it is the difference between fixing it yourself and carrying it to a shop.

When you need one

Four situations, and the first two are the common ones.

The computer will not start. Windows will not load, you are stuck on a repair loop, or the screen never gets past the manufacturer's logo. A bootable drive gets you to a working environment where you can run repairs or, at minimum, copy your files off before doing anything drastic.

You want a clean reinstall. Sometimes a machine is so tangled that starting again is faster than fixing it. A Windows installation drive lets you do that properly, including wiping and repartitioning the disk.

You want to test hardware. Memory tests and drive diagnostics run from a bootable drive so they can examine hardware without Windows in the way.

You want to try another operating system. Most Linux distributions can run directly from the USB drive without installing anything, which is a genuinely risk-free way to look around.

Make it now, not later

This is the entire point and it is worth being blunt about it. A recovery drive made after the computer has failed is not possible, because you need a working computer to make one.

If you have a second machine you can borrow, fine. Plenty of households do not, and the failure always happens at the least convenient moment. Fifteen minutes today, on a USB stick you already own, removes that problem permanently.

Making one

You need a USB drive of at least 8 GB, and 16 GB is more comfortable. Everything on it will be erased, so check it first.

For Windows installation media, Microsoft provides a tool that downloads the current version and writes the drive for you in one step. Search for the Windows Media Creation Tool on Microsoft's own site, run it, and choose the option to create installation media for another PC. It handles the technical details itself.

For a Windows recovery drive, which repairs your existing installation rather than replacing it, Windows has this built in. Search the Start menu for Create a recovery drive. Tick the option to back up system files, which makes the drive larger but far more useful, and let it run. This is the one to make if you only make one.

For anything else, you will have a disc image file, usually with an .iso extension, and you need a tool that writes it to the drive correctly. Copying the file onto the USB stick does not work, because a bootable drive needs a particular structure that a plain copy does not create.

The settings that catch people out

Two technical choices appear when writing a drive, and picking wrong means the computer simply will not see it.

If you are unsure, GPT and UEFI are correct for essentially any computer bought in the last decade. If the drive does not appear in the boot menu, this pair is the first thing to change.

Actually booting from it

Computers start from their internal drive by default, so you have to tell yours otherwise. There are two ways.

The quick way is the one-time boot menu. Press a key repeatedly as the machine starts, and choose the USB drive from a list. The key varies by manufacturer, and the usual candidates are F12, F11, F9 and Escape. Many machines show it briefly on the startup screen. This changes nothing permanently, which makes it the better option.

The other way is changing the boot order in the firmware settings, usually reached with Delete or F2 at startup. This makes the machine always check USB first, which is fine but easy to forget about later.

If the drive still does not appear, check three things. It should be plugged into a port directly on the machine rather than through a hub. A USB 2 port sometimes works when a USB 3 one does not, particularly with older installation media. And Secure Boot may need to be disabled temporarily for some non-Microsoft tools, though official Windows media works with it left on. Turn it back on afterwards.

What to do once you are in

If you booted because the machine will not start, resist the urge to reinstall immediately. Copy your files off first. A recovery environment gives you a file browser and access to the drive, and an external disk is all you need. Whatever you do next is safer once your documents and photographs are somewhere else.

Only after that is done should you try repairs or a reinstall. The order matters, because a repair that goes wrong at that point costs you nothing you cannot replace.

Keep the finished drive somewhere you will find it, and label it with what it is and the date. A recovery drive made three Windows versions ago still boots, but it is worth refreshing once a year. Write the date on it and that decision becomes easy instead of a guess.