Non-Uniform Memory Access (NUMA) is a modern approach to server memory design. Contemporary multiprocessor servers consist of several isolated one-socket computers joined together on one motherboard. Each processor has its own memory slots and only this processor has access to memory installed in these slots. The same way each processor has its own PCI-E bus where other devices connect.

Processors request each other's devices and memory through a high-speed bus. It connects all the available processors, and access to the CPU's own memory is faster than access to memory that belongs to other processors.

vSphere 5 is NUMA-aware and when possible, it places vCPUs on physical processors that own the VM's memory. It is important to consider NUMA requirements when managing your infrastructure.