A bootable USB drive contains an operating system image or tool written in a way that the computer firmware (BIOS or UEFI) can start it. It is created by writing an ISO image to the drive with a tool such as Rufus, balenaEtcher or the dd command, not by copying the file normally.
Why it matters
It is the standard way to install Windows or Linux, run a live system without changing the disk, reset a forgotten local password or run diagnostics when the installed system will not start. The computer must be told to boot from USB, usually through a one-time boot menu key such as F12, F10 or Esc, which varies by manufacturer.
Example
On Linux, writing an ISO to a stick at /dev/sdb:
sudo dd if=ubuntu.iso of=/dev/sdb bs=4M status=progress conv=fsyncThis erases everything on the stick. Choosing the wrong device, such as your system disk, would destroy data, so verify with lsblk first.
Common mistakes
- Dragging the ISO onto the drive as a normal file.
- Writing to the wrong disk.
- Forgetting Secure Boot or the boot mode (UEFI vs legacy) when the stick does not show up.
Related
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