These are internally linked to form a fat tree topology. Like other interconnects such as Myrinet very large systems can be built by using multiple switch chassis arranged as spine (top-level) and leaf (node-level) switches. Such systems were called "federated networks". It was announced in 1998 and used PCI 66-64 cards that had 'elan3' Custom ASIC on them. These gave an MPI bandwidth of around 350 Mbyte/s unidirectional with 5us latency. QsNet II was the fourth and penultimate generation of Quadrics Interconnect family products, and was launched in 2003. QsNetII interfaced to the host computer through the standard IO PCI-X bus. Later versions of the card had PCIe physical interfaces although this was bridged on the card to PCI-X with a performance penalty. A native PCIe version was never developed. Instead resource was focused on QsNetII's successor QsNetIII which although completed was never released commercially.. The architecture of the network interface has been developed to offload the entire task of interprocessor communication from the main processor, and to avoid the overhead of system calls for user process to user process messaging. QsNetII is designed for use within SMP systems — multiple, concurrent processes can utilise the network interface without any task switching overhead. A I/O processor offloads protocol handling from the main CPU. Local memory on the PCI card provides storage for buffers, translation tables and I/O adapter code. All the PCI bandwidth is available to data communication. QsNetII's core design is based on two ASICs: Elan4 and Elite4. Elan4 is a communication processor that forms the interface between a high-performance multistage network and a processing node with one or more CPUs. Elite4 is a switching component that can switch eight bidirectional communications links, each of which carrying data in both directions simultaneously at 1.3 GB/s. Quadrics QsNetII interconnect like its predecessor QsNet uses a 'fat tree' topology, QsNetII scales up to 4096 nodes, each node might have multiple CPUs so that systems of >10,000 CPUs can be constructed. Multiple, parallel QsNet networks can be employed in a system to maintain the compute to communications ratio where high CPU count SMP nodes are employed. The fat tree topology is resilient with large amounts of redundancy in the higher levels of the switch. Performance depends on platform used and configuration of the system, QsNetII MPI latency on standard AMD Opteron starts at 1.22 μs; Bandwidth on Intel Xeon Intel 64 is 912 MB/s.