As someone who only runs Linux, I occasionally need to run DOS for updating the BIOS on various machines.
Floppy disks are no more an option, since it has been nearly two decades with machines not shipping with them. Therefore, the only realistic option is using USB flash drives.
One excellent alternative to Microsoft MS-DOS, is FreeDOS, a free clone that needs very little resources to run. It can be used to run legacy applications, and one of them is flashing a new BIOS.