If you have an old PC that doesn’t support booting from USB to do that you can use Plop Boot Manager, a small piece of software that allows you to boot from USB, shortly you need to download plpbt, unzip and burn plpbt.iso to a CD and boot from it. In this example we will use VirtualBox, the current version (5.1.26) does not support USB booting.
Boot from USB in VirtualBox
1. Download plpbt, unzip and mount plpbt.iso
2. Open “Settings” go to USB and enable “USB 1.1 (OHCI) Controller”
3. Start the virtual machine and attach the USB flash drive from Devices -> USB
4. Reset the virtual machine, Plop Boot Manager should appear and select “USB”