Some volume managers also implement snapshotting by applying copy-on-write (COW) to each PE. In this scheme, the volume manager will copy a PE to a "COW table" just before it is written to. This preserves an old version of the LE—the "snapshot"—which can later be reconstructed by overlaying the copy-on-write table on the current LE. Snapshots which are read-write are "branching snapshots" because they implicitly allow diverging versions of an LE.