You cannot turn a USB drive into a CD, but you can make a USB drive behave like one by writing an ISO file to it. An ISO file is a complete copy of a disc's contents packaged into a single file. When you write an ISO to a USB drive using the right tool, the drive becomes bootable — meaning your computer can start up from it — and it works almost identically to the original CD or DVD. This is useful when you want to install Windows, Linux, or other software on a computer without a disc drive, or when you want to create a backup copy of a disc you own.

Key Takeaways

  • You need an ISO file (a disc image) and free software like Rufus, Etcher, or Windows' built-in Media Creation Tool to write it to the USB drive.
  • Writing an ISO to a USB drive erases everything on that drive, so back up any files you want to keep before you start.
  • The USB drive must be at least as large as the ISO file — a 4 GB ISO needs a USB drive with at least 4 GB of free space.
  • After writing the ISO, the USB drive will boot on most computers, but some older machines may need you to change the boot order in BIOS settings.

Get the ISO File You Need

Before you can write anything to a USB drive, you need the ISO file itself. If you are trying to install Windows, you can download the ISO directly from Microsoft's website at no cost — go to microsoft.com/software-download and choose your Windows version. If you are installing Linux, visit the distribution's official website (Ubuntu, Fedora, Debian, and others all offer free ISO downloads). If you are working with a disc you already own, you can create an ISO from it using free software like ImgBurn or Brasero, but you must own the original disc.

Save the ISO file somewhere you can find it easily, like your Downloads folder or Desktop. Note the file size — you will need a USB drive with at least that much free space, plus a little extra.

Choose and Install the Writing Software

The tool you use depends on your operating system. Rufus is the most popular choice for Windows and works with almost any ISO. Etcher (also called Balena Etcher) works on Windows, Mac, and Linux and is simpler to use if you are new to this. Windows 10 and 11 also include a built-in Media Creation Tool specifically for Windows installation ISOs, which requires no separate download.

For Windows, download Rufus from rufus.ie or Etcher from balena.io/etcher. Neither requires installation — you download the file and run it directly. For Mac, download Etcher the same way. For Linux, Etcher is available through your package manager (Ubuntu users can search "Etcher" in the Software Center), or download it from the website.

Back Up Your USB Drive Before Writing

Writing an ISO file to a USB drive erases everything on it. If the drive contains files you need, copy them to your computer first. Plug in the USB drive, open File Explorer (Windows) or Finder (Mac), and drag any important files to a folder on your computer. Once they are safely copied, you can proceed.

After you back up your files, eject the USB drive properly — right-click it in File Explorer and choose "Eject", or drag it to the Trash on Mac. Wait a few seconds, then unplug it and plug it back in. This ensures the drive is in a clean state before writing.

Write the ISO to the USB Drive Using Rufus or Etcher

Using Etcher (simplest method): Open Etcher, click "Select Image", and choose your ISO file. Click "Select Target" and choose your USB drive — the software shows you the drive's size so you can confirm you picked the right one. Click "Flash" and wait. The process usually takes 5 to 15 minutes depending on the file size. When it finishes, Etcher tells you the write was successful.

Using Rufus (Windows): Open Rufus, and the USB drive should already be selected in the "Device" dropdown at the top. Click the disc icon next to "Boot Selection" and choose your ISO file. Leave the other settings at their defaults — Partition Scheme should be "MBR" for older computers or "GPT" for newer ones (if unsure, leave it as is). Click "Start" and confirm the warning that the drive will be erased. Rufus writes the file and shows a progress bar. When it finishes, close the window.

Using Windows Media Creation Tool (Windows only, for Windows ISOs): Open the tool, choose "Create installation media for another PC", select your language and Windows version, choose "USB flash drive", select your USB drive from the list, and click "Next". The tool downloads and writes the ISO automatically.

Verify the USB Drive Works

After writing is complete, safely eject the USB drive and plug it into the computer where you want to use it. Restart that computer and watch for a prompt to "Press any key to boot from USB" or similar — this usually appears for a few seconds before the computer tries to start normally. Press any key when you see it, and the USB drive should boot.

If nothing happens and the computer starts normally, you may need to change the boot order in BIOS. Restart the computer and immediately press Delete, F2, F10, or F12 (the key varies by manufacturer — watch the startup screen for a message like "Press F2 to enter Setup"). Look for a "Boot Order" or "Boot Sequence" menu, move the USB drive to the top of the list, save, and restart. The USB drive should now boot.

Troubleshooting Common Problems

If the USB drive does not boot, the most common cause is that the ISO was not written correctly. Plug the drive back into your original computer and run the writing software again, making sure you selected the correct ISO file and USB drive. Some older computers cannot boot from USB at all — if yours is more than 10 years old, check its manual or manufacturer's website to confirm USB boot is supported.

If the writing software says "Access Denied" or "Permission Denied", close the software, right-click it, and choose "Run as Administrator" (Windows) or enter your password when prompted (Mac and Linux). If the software cannot find your USB drive, unplug it, wait 10 seconds, and plug it back in, then restart the software.

If the USB drive appears to have no files after writing, that is normal — the ISO is written as a bootable image, not as regular files. The drive will show as having used space, but you will not see folders or documents. This is correct and means the write succeeded.

Frequently Asked Questions

Can I use the USB drive for other files after writing an ISO to it?

Not easily. Once an ISO is written to a USB drive, the entire drive is formatted as a bootable disc image. To use it for regular files again, you must reformat it — right-click the drive in File Explorer, choose "Format", and select "FAT32" or "NTFS". This erases the ISO and restores the drive to normal use.

What size USB drive do I need?

The drive must be at least as large as the ISO file. Windows 10 and 11 ISOs are typically 5 to 6 GB, so an 8 GB USB drive is the minimum. Linux ISOs are usually 2 to 4 GB, so a 4 GB drive works. Check the ISO file size before you start — right-click it and look at the "Size" property.

Do I need to eject the USB drive after writing the ISO?

Yes. Always eject the drive through File Explorer or Finder before unplugging it. This ensures all data is written and prevents corruption. Right-click the drive and choose "Eject" or "Safely Remove Hardware".

Will this work on a Mac or Linux computer?

Yes. Etcher works on all three operating systems. Rufus is Windows-only, but Mac users can use Etcher or the command line tool dd, and Linux users have Etcher, dd, or GNOME Disks built in.

Can I write multiple ISO files to one USB drive?

Not with the standard method described here. Each ISO write erases the previous one. If you want multiple bootable ISOs on one drive, you need specialized tools like Ventoy, which is more advanced and requires extra steps.