The build .tbz2 file is a minimal set of system files that is necessary for allowing a user to bootstrap and install Gentoo Linux. The build .iso is a complete, bootable CD image that contains a system kernel, a reasonably complete set of kernel modules, necessary system tools such as mkfs and networking support, as well as the .tbz2 minimal-system tarball. Most users will install Gentoo Linux by burning the .iso file onto a CD, booting off of the CD, and installing from within the minimal linux environment provided by the Gentoo boot CD. It is possible, however, for users to install Gentoo Linux directly from an already-existing Linux distribution. Such users need only download the .tbz2 file, install the contents on a spare partition (making sure to use the p flag when untarring the tarball!), chroot, and install in the usual fashion.