FreeDOS is a complete operating system. For new users, we recommend installing FreeDOS in a PC emulator or “virtual machine.” If you install FreeDOS directly on a computer, without using a PC emulator, you may overwrite the operating system you have now (for example, Windows.) Please be careful.

How much space do you need? At minimum, you need at least 10MB to install just Base, without source code. Or at least 81MB to install everything, including source code.

If your computer doesn't have a CDROM drive, use the USB fob drive installer. Write this to a USB fob drive and boot it to start the install. The “Full” and “Lite” versions install the same FreeDOS, but the “Lite” installer does not contain some extra bonus software packages.

http://freedos.org/