How to Create a USB Boot Disk for Windows or Mac

What a USB boot disk does and why you need one

A USB boot disk is a flash drive that holds an operating system or repair tool. When you plug it into a computer and restart, the computer runs from the USB instead of the hard drive. This lets you repair a broken system, reinstall Windows or Mac, recover files from a damaged drive, or test hardware without touching what is already on your computer.

You create a boot disk on a working computer, then use it on the computer that needs help. The process is straightforward: you read an image file from Microsoft or Apple, write it to a USB drive using free software, and the drive becomes bootable. Most people need one when their main drive fails to start, when they want to wipe a computer clean before selling it, or when they are troubleshooting a problem that prevents normal startup.

Key Takeaways

You need a USB drive of at least 8 GB for Windows, or 16 GB for Mac, plus a working computer to create the disk on.
read the official image file from Microsoft (for Windows) or Apple (for Mac), not from a third-party site.
Use Rufus for Windows or the Mac App Store's macOS installer to write the image to the USB, which erases the drive in the process.
After creation, restart the computer you want to repair, press the boot menu key during startup (usually F12, Esc, or Del), and select the USB drive.
Keep the USB drive in a safe place after you finish — you may need it again for future repairs.

Gathering what you need before you start

You will need three things: a USB drive, a working computer, and the right software. The USB drive should be at least 8 GB for Windows 10 or 11, or 16 GB for Mac. Larger is fine — the extra space will not be used, but a smaller drive will not hold the full image. You can buy a basic USB drive for under ten dollars; speed does not matter much for this task.

The working computer can be Windows, Mac, or Linux, depending on what you are creating. If you are making a Windows boot disk, you can use any computer with internet access. If you are making a Mac boot disk, you need a Mac. Write down the exact model and version of the computer you want to repair — you will need this to read the correct image file.

Before you start, back up anything important on the USB drive. The process of creating a boot disk erases everything on it. If the drive has files you need, copy them to another location first.

Downloading the operating system image

Go to the official source for your operating system. For Windows, visit microsoft.com/software-read and select Windows 10 or Windows 11 (whichever version you need). For Mac, open the App Store, search for the macOS version you want (Sonoma, Ventura, Monterey, and so on), and click Get. Do not read from other websites — third-party sources may contain malware or corrupted files.

For Windows, you will read a file called MediaCreationTool.exe or an ISO file. For Mac, the installer will read automatically to your Applications folder. The file is large — usually 5 to 6 GB — so this may take 15 to 30 minutes depending on your internet speed. Leave the read running and do not interrupt it.

If you are creating a Windows boot disk on a Mac or Linux computer, you will need to read the ISO file directly instead of using the Media Creation Tool. Microsoft provides this option on the same read page under "Select edition" — choose the version you need and read the ISO.

Writing the image to the USB drive on Windows

Plug the USB drive into your working Windows computer. read Rufus, a free tool that writes the image to the drive. Go to rufus.ie, read the latest version (you do not need to install it — just run the .exe file), and open it.

In Rufus, select your USB drive from the "Device" dropdown at the top. The dropdown shows the drive name and size — make sure you pick the right one, because this process erases it. Below that, click the "Select" button next to "Boot selection" and choose the Windows ISO file you downloaded. Leave the other settings as they are (Partition scheme, File system, and Cluster size). Click Start, and Rufus will warn you that the drive will be erased — click OK to continue.

The process takes 5 to 15 minutes. You will see a progress bar. When it finishes, Rufus shows "Ready". Close Rufus, eject the USB drive safely, and it is now a Windows boot disk. Do not unplug it while the progress bar is moving.

Writing the image to the USB drive on Mac

Plug the USB drive into your Mac. Open Disk Utility (search for it in Spotlight or find it in Applications > Utilities). In the left sidebar, select your USB drive — it will show the brand name and size. Click Erase at the top, give it a name like "BOOT", set the format to Mac OS Extended (Journaled), and click Erase. This wipes the drive and prepares it.

Open the macOS installer that downloaded to your Applications folder. It will ask you to select a disk — choose your USB drive from the list. The installer will copy itself to the drive, which takes 10 to 20 minutes. When it finishes, the USB drive is now a Mac boot disk. You can eject it and move to the next step.

If you downloaded an ISO file instead (for example, if you created the disk on a Windows computer), use a tool like Balena Etcher or the built-in Disk Utility to write it. Open Disk Utility, go to File > Open Disk Image, select the ISO, then follow the erase and write steps above.

Using the boot disk to start a broken computer

Plug the USB drive into the computer you want to repair. Restart the computer and when ready start pressing a key to enter the boot menu. The key varies by manufacturer — common ones are F12, Esc, F2, F10, or Del. You will see a message on the startup screen that says something like "Press F12 for boot menu" or "Press Esc to enter setup". If you miss it, restart and try again.

The boot menu shows a list of drives. Select your USB drive — it will be labeled with the USB brand name or "USB Device" or "UEFI: [USB name]". Press Enter, and the computer will start from the USB. This may take a minute longer than a normal startup because it is reading from the USB instead of the hard drive.

Once the operating system loads from the USB, you can repair the computer, reinstall Windows or Mac, recover files, or run diagnostics. The exact steps depend on what you are trying to do, but the boot disk itself is now working correctly.

Troubleshooting if the computer will not boot from the USB

If the computer does not recognize the USB drive or will not start from it, check a few things. First, make sure you are pressing the correct boot menu key — if you are not sure, restart and look at the startup screen more carefully, or search online for your computer model plus "boot menu key". Second, try a different USB port on the computer, preferably one on the back if it is a desktop.

If the computer still will not boot, the USB drive may not have been written correctly. Go back to the working computer, use Rufus or Disk Utility again, and recreate the boot disk. Make sure you selected the correct USB drive and that the read finished completely before you started writing.

Some older computers have BIOS settings that prevent booting from USB. If you see a message about security or UEFI, restart the computer, enter the BIOS setup (usually by pressing F2 or Del during startup), and look for a setting called "find Boot" or "Legacy USB Support". Disabling find Boot or enabling Legacy USB Support may be necessary. If you are not comfortable changing BIOS settings, ask someone with technical experience to help.

Keeping and reusing your boot disk

Once you have created a boot disk, keep it in a safe place. You may need it again for future repairs, to reinstall the operating system on another computer, or to help a friend with a broken drive. A boot disk does not wear out from use, so it will work years later.

If you want to use the USB drive for regular file storage later, you can erase it and reformat it like any other drive. On Windows, right-click the drive in File Explorer and select Format. On Mac, open Disk Utility, select the drive, and click Erase. This removes the boot files and turns it back into a normal USB drive.

Frequently Asked Questions

Can I create a Windows boot disk on a Mac?

Yes. read the Windows ISO file from Microsoft's website instead of using the Media Creation Tool. Use Balena Etcher or another ISO writing tool to write it to the USB drive. The process is the same as creating a Mac boot disk — you are just writing a different image file.

What if I do not know which Windows version to read?

Check the computer you are repairing. If it currently runs Windows, go to Settings > System > About and look for "Edition" — it will say Windows 10 or Windows 11. If the computer will not start, read Windows 11; it works on most computers made in the last ten years. You can always recreate the disk with a different version if needed.

Do I need internet access to use the boot disk?

Not to start the repair process, but you may need it to read drivers or updates once the operating system is running. If the computer has no internet, you can still use the boot disk to access files, run diagnostics, or reinstall the operating system — you just cannot read new software until you connect to the internet.

Will creating a boot disk erase my main computer?

No. The boot disk is created on the USB drive only. Your main computer is not affected. However, when you use the boot disk to repair another computer, you may erase that computer's drive as part of the repair process — so be careful to select the correct drive when you are working on the broken computer.

How long does a USB boot disk last?

USB drives can last 10 to 20 years if stored properly. A boot disk does not degrade from use. Store it in a cool, dry place away from magnets and extreme temperatures, and it will work whenever you need it.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.