IBM RedBooks department released a nice small paper about NUMA architecture on xSeries:
Abstract
There are currently two main concepts related to connecting processors and memory together in a multi-processor system. One way of achieving multi-processor scalability is using symmetrical multiprocessing or SMP, and the other way is using non-uniform memory access or NUMA. SMP has been in use in xSeries-class servers since the early days. However, NUMA has only appeared in commercial xSeries servers over the past few years. This document introduces the concepts behind NUMA and explains the benefits.
Yes, I know this isn’t directly related to virtualization topics, but since IBM xSeries are a preferred platform for virtualization environments, I think someone could appreciate.