Each XT5 compute node has two NUMA nodes (see Figure 1) and each XT4 compute node has one NUMA node. A NUMA node is a quad-core processor (see Hardware overview of Louhi and Processor architecture) and its local memory.  This means that it is possible to run one application per NUMA node. It enables two applications on a same XT5 compute node. Also applications can execute using both NUMA nodes of a Cray XT5 compute node. The application processes allocate local NUMA node memory first. If there is not free local NUMA node memory available, the allocation may be satisfied using remote NUMA node memory. The total memory available for an application on a compute node is little less than installed amount of memory. Because the compute nodes on the XT5 part have 8 or 16 GB memory the new system has better support for more memory intensive applications.

Figure 1