A bootable flash drive will allow you to boot the computer from the file system on the flash drive rather than your hard drive. ... In order for us to boot to a flash drive, it must have a master boot record, volume boot record, and contain an operating system or a program that can be executed.

Is bootable USB necessary?

They're missing the “master boot record” (MBR) that's absolutely necessary for booting most PCs (specifically those with a “basic input/output system” (BIOS)). You have to make a new USB stick bootable on your own.

What is bootable media USB drive?

An optical disc (CD, DVD) or USB drive that contains a bootable program that takes control of the computer. ... The computer can also be configured to look for the USB drive first, although very early computers do not have that option.