
USB image

A USB image — is bootable image of Operating system (OS) or other software where the boot loader is located on a USB flash drive, or another USB device (with memory storage) instead of conventional CD or DVD discs. The operating system loads from the USB device either to load it much like a Live CD that runs OS or any other software from the storage or installs OS itself. USB image runs off of the USB device the whole time. A USB image is easier to carry, can be stored more safely than a conventional CD or DVD. Drawbacks are that some older devices may not support USB booting and that the USB storage devices lifespan might be shortened.
Ubuntu has included a utility for installing an operating system image file to a USB flash drive since version 9.10. Windows support also has added a step by step on how to set up a USB device as a bootable drive.
Software.
Both graphical applications and command line utilities are available for authoring bootable operating system images. dd is a utility commonly found in Unix operating systems that allow creation of bootable images.