A torus interconnect is a network topology for connecting processing nodes in a parallel computer system. It can be visualized as a mesh interconnect with nodes arranged in a rectilinear array of N = 2, 3, or more dimensions, with processors connected to their nearest neighbors, and corresponding processors on opposite edges of the array connected. The lattice has the topology of an N dimensional torus and each node has 2N connections.
A number of supercomputers on the TOP500 list use three-dimensional torus networks, e.g. IBM's Blue Gene/L and Blue Gene/P, and the Cray XT3. IBM's Blue Gene/Q uses a five-dimensional torus network. Fujitsu's K computer and the PRIMEHPC FX10 use a proprietary six-dimensional torus interconnect called Tofu.
- In a two-dimensional torus interconnect, the nodes are imagined laid out in a two-dimensional rectangular lattice of rows and columns, with each node connected to its 4 nearest neighbors, and corresponding nodes on opposite edges connected. The connection of opposite edges can be visualized by rolling the rectangular array into a "tube" to connect two opposite edges and then bending the "tube" into a torus to connect the other two.
- In a three-dimensional torus interconnect the nodes are imagined in a three-dimensional lattice in the shape of a rectangular prism, with each node connected with its 6 neighbors, with corresponding nodes on opposing faces of the array connected.
Higher-dimensional arrays can't be directly visualized, but each higher dimension adds another pair of nearest neighbor connections to each node.
While long wrap-around links may be the easiest way to visualize the connection topology, in practice, restrictions on cable lengths often make long wrap-around links impractical. Instead, directly connected nodes -- including nodes that the above visualization places on opposite edges of a grid, connected by a long wrap-around link -- are physically placed nearly adjacent to each other in a folded torus network. Every link in the folded torus network is very short -- almost as short as the nearest-neighbor links in a simple grid interconnect -- and therefore low-latency.
- Industrial Strength Parallel Computing by Alice E. Koniges 1999 ISBN 1-55860-540-1 page 16
- N. R. Agida et al. 2005 Blue Gene/L Torus Interconnection Network, IBM Journal of Research and Development, Vol 45, No 2/3 March–May 2005 page 265 
- Fujitsu Unveils Post-K Supercomputer HPC Wire Nov 7 2011
- Cray Inc. "The Gemini Network". 2010. p. 13.
- "Small-World Torus Topology".
- Pavel Tvrdik. "Topics in parallel computing: Embeddings and simulations of INs: Optimal embedding of tori into meshes".
- "The 3D Torus architecture and the Eurotech approach".
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