(original article from: http://www.howtogeek.com/136987/how-to-create-a-bootable-dos-usb-drive/)
DOS isn’t widely used anymore, but you wouldn’t know if from reading instructions written by manufacturers for BIOS updates, firmware-updating utilities, and other low-level system tools. They will often require you to boot into DOS and run the utility.
We once formatted our floppy disks with MS-DOS using the format utility built into Windows, but most computers don’t have floppy disk drives anymore. They may not even have optical disc drives!
Windows won’t allow you to select the “Create an MS-DOS startup disk” option when formatting a USB drive – it’s grayed out. We will be using Rufus instead. It’s a fast, lightweight application that includes FreeDOS.
Download Rufus and launch it. Rufus doesn’t require any installation – you will see the Rufus application as soon as you launch the downloaded .exe file.
Creating a bootable USB drive with DOS is simple:
- Connect your USB drive to the computer and select it in the Device box.
- Ensure the “Create a bootable disk using” checkbox is enabled and ensure FreeDOS is selected. (Rufus includes FreeDOS, so you won’t have to download anything else.)
- Click the Start button. This will erase the contents of your USB drive! Back up any important files on the USB drive first.
These should be the default options, so you may not even have to configure Rufus at all. The process should be extremely quick – it took five seconds on our system.
Copy Your Files Over
You have probably created this boot drive because you have a DOS-based program to run, such as a BIOS update utility or another low-level system program. To actually run these files from DOS, you will need to copy them over to your USB drive. For example, you may have a BIOS.BIN and FLASHBIOS.BAT file you need to run in DOS. Copy these files into the root directory of the USB drive after formatting it.
Boot Into DOS
You can now boot into DOS by restarting your computer. If your computer does not automatically boot from the USB drive, you may need to change your boot order or use a boot menu to select the device you want to boot from.
Once you are in DOS, you can run the program you copied to your USB drive by typing its name at the DOS prompt. Follow any instructions provided in the manufacturer’s documentation to run the application.
These utilities still use DOS to ensure they have low-level access to the hardware without any other programs interfering or Windows getting in the way. This helps ensure BIOS updates and other low-level operations work properly.
You could use a bootable USB drive to run old DOS applications, but you would be better off using DOSBOX to run old DOS games and other applications.