Free and open source software didn’t invent Live Disks (external CDs, DVDs, or flash drives from which you can boot a computer). That honor, according to Wikipedia, goes to FM Towns OS in 1989.
However, no other segment of IT has made Live Disks so much a part of their culture as the open source community.
Most major Linux distributions use Live Disks for installation because they are a quick way to test-drive an operating system without changing a computer’s setup or endangering its contents. When using a Live Disk, at worst, you may need to reset the BIOS temporarily to boot from an external device, and users have to set about deliberately to alter files on the hard drive.
Live Disks are especially handy for checking hardware support on a machine before purchasing — assuming, that is, you can find a store clerk who knows what Live Disks are and has no fear that they might contain malware.