The support provided by IRAF for layered software is essentially the same as that provided for maintaining the core IRAF system itself (the core system is a special case of a layered package). Each layered package (usually this refers to a suite of subpackages) is a system in itself, similar in structure to the core IRAF system. Hence, there is a LIB, one or more BINs, a help database, and all the sources and runtime files. A good example of an external package is the NOAO package. Except for the fact that NOAO is rooted in the IRAF directories, NOAO is equivalent to any other layered product, e.g., STSDAS, TABLES, XRAY, CTIO, NSO, ICE, GRASP, NLOCAL, STEWARD, and so on. In general, layered products should be rooted somewhere outside the IRAF directory tree to simplify updates.