Rootfs.img

  is a file containing an ext2 filesystem that XDAndroid mounts (read-only) at.

provides:
 * essential UNIX utilities such as  and
 * the Radio Interface Layer (RIL)
 * mount points for other XDAndroid filesystems:
 * (see )
 * (see )
 * keyboard keymaps
 * (see )
 * keyboard keymaps
 * keyboard keymaps

images are not specific to a particular release of Android. I.e. a given  image may work with Donut, Eclair, and Froyo.

is generally stored in the  directory of the SD card.