Suitable backup media include an external hard drive
(best option), a memory
card (like the kind you use in a camera), a flash
drive, and
DVD-R or CD-R (worst option). Removable
media
(such as discs, memory cards, and flash drives) are marked as
unsuitable for a system
image,
but that's something different than a backup, so you're okay to use
those here.
If [Recommended] appears next to one
of the choices,
that's the one you should use. If none is recommended, choose the media
with the most free space. If the Save Backup On list box is empty, you
don't a device to back up to. Attach
or insert the backup media you intend to use and click the Refresh
button.