# IB single-plane topology A complete M-Cell assembly consists of four compute racks. Each rack contains 4 x physical IRUs - Independent rack units. Using one dual socket node per one blade slot leads to 8 logical IRUs. Each rack contains 4 x 2 SGI ICE X IB Premium Blades. The SGI ICE X IB Premium Blade provides the first level of interconnection via dual 36-port Mellanox FDR InfiniBand ASIC switch with connections as follows: * 9 ports from each switch chip connect to the unified backplane, to connect the 18 compute node slots * 3 ports on each chip provide connectivity between the chips * 24 ports from each switch chip connect to the external bulkhead, for a total of 48 ## IB Single-Plane Topology - ICEX M-Cell Each color in each physical IRU represents one dual-switch ASIC switch. [IB single-plane topology - ICEX Mcell.pdf](<../src/IB single-plane topology - ICEX Mcell.pdf>)  ## IB Single-Plane Topology - Accelerated Nodes Each of the 3 inter-connected D racks are equivalent to one half of M-Cell rack. 18 x D rack with MIC accelerated nodes [r21-r38] are equivalent to 3 M-Cell racks as shown in a diagram [7D Enhanced Hypercube](7d-enhanced-hypercube/). As shown in a diagram [IB Topology](7d-enhanced-hypercube/#ib-topology) * Racks 21, 22, 23, 24, 25, 26 are equivalent to one M-Cell rack. * Racks 27, 28, 29, 30, 31, 32 are equivalent to one M-Cell rack. * Racks 33, 34, 35, 36, 37, 38 are equivalent to one M-Cell rack. [IB single-plane topology - Accelerated nodes.pdf](<../src/IB single-plane topology - Accelerated nodes.pdf>) 