USB Boot Drive
Many people are not aware that it is possible to run an operating system on a USB flash drive (USB boot drive). It is additionally possible to boot from USB flash drives directly, but in this case, you are only utilizing the computer BIOS at startup and the operating system installed on the computer does not load allowing you to easily launch an operating systems from the flash drive if it is large enough. These USB boot drives are commonly referred to as Live USBs. Generally, many people boot Linux from USB drives, but most operating systems are available through this method. It is possible to utilize both Windows and Mac OS on a Live USB.