We have added several packages to Scientific Linux 4.8 that were not in the Scientific Linux 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, or 4.7 releases.

squashfs
Summary : Squashfs is a compressed read-only filesystem for Linux.
This is not installed by default.

unionfs
Summary : Unionfs builds a stackable unification file system, which can appear to merge the contents of several directories (branches), while keeping their physical content separate.
This is not installed by default.