The Fat-Tree network, invented by Charles Leiserson of MIT, is a universal network for provably efficient communication. Unlike an ordinary computer scientist's notion of a tree, which is skinny all over, the links in a fat-tree become "fatter" as one moves up the tree towards the root. By judiciously choosing the fatness of links, the network can be tailored to efficiently use any bandwidth made available by packaging and communication technology. In contrast, most communication networks, such as hypercubes and meshes, have communication requirements that follow a prespecified mathematical law, and therefore cannot be tailored to specific packaging technologies. The Connection Machine Model CM5 Supercomputer (circa 1990) used a fat-tree interconnection network, and it is now the preferred network for the Infiniband cluster architecture.