Shown on the left is an Apple Saw 4 chipset in a single package. This architecture was developed by Alpine Microsystems to address "known good die" and 3D packaging. The year was 1998 and the industry did not have 3D packaging. Through Silicon Vias were not ready for prime time and Alpine's silicon on silicon on silicon architecture was developed to allow any ordinary set of chips to be packaged together. Also, at this time, there weren't any 3D CAD tools, let alone process tools.