"But what if your computer doesn't have a working CD
drive? Well, no problem. Ubuntu Live can also boot and install
itself from an USB thumb drive or an SD card (henceforth, for
simplicity's sake, "USB drive"). All you need is a drive that is
1GB or bigger.
"Problem is, not everybody can use the famous liveusb program to
create bootable live USB drives. Some of us are using Fedora on our
workstations. Others might actually want to run Knoppix or another
live distribution, not Ubuntu. Yet others might not like the way
liveusb partitions the disk space in your USB drive, or might want
extra functionality not provided by it."