In NUMA architecture, or non-uniform memory access, multiple processors in a computer system are grouped. They are usually called Quads, or Node Cards as in SGI servers, and the quads have their own memory and I/O controller. Quads are connected by high-speed interconnects. Unlike a cluster, all these quads are part of a single node. Thus, a NUMA system can be thought of as a large SMP system. However, the memory is non-uniformly distributed to the processors, each quad has its own localized memory, but the memory is accessible to other quads. To the processors, all of the memory in a NUMA machine appears same, but the only difference is in access time. NUMA is also called Distributed shared memory (DSM) architecture.  

Good examples for NUMA systems include the Sequent (now IBM) servers and Silicon Graphics (SGI) 2000 / 3000 series.

Emerging Server Cluster Architectures

Any server requires power, connectivity to storage and to an IP network. When the servers are clustered, it usually requires a redundant heartbeat and cluster-management connection, and potentially redundant connections to dual ported storage. As a cluster begins to grow and have many nodes, with cables and connectors of the physical environment, it becomes very complex and messy. Having cluster architecture may result in many points of failure. It can be a real nightmare situation for data center managers.

The concept of the Bladed Server or Blade Server is gaining wider acceptance as it helps to solve the complexities of cluster management and also provides a modular solution to the growth of servers.

The BladeFrame architecture provides hot insertion and removal of servers, which are also called blades, and cable consolidation. Process Area Network (PAN) manager software handles the external storage mapping and virtualization, and the control of I/O and network traffic to and from individual servers. The Blade Server provides a specially designed rack into which the blades fit - the idea is to save space and power, reduce cabling, and simplify maintenance and expansion.

Thus, the main features of the Blade Technology include:

* BladeFrame is a collection of Blades

* Infrastructure of Networking and Storage Connectivity is built-in

* Infrastructure of Networking and Storage Connectivity is common to all the blades in the frame

* Power Supply is common but preferably from multiple sources

* Each blade can act as a database or application server or as a client host

* Each server can have its own flavor of operating system such as Linux or Windows

* Each server can be put to use for any number of things including Load Balancer, FireWall, App. Server, DB server, etc.

* All the components are housed in a rack.

The Blade technology based server farm is available from Egenera, IBM, HP, Dell etc. As an example, the BladeFrame system from Egenera allows for a pool of up to 96 high-end Intel? processors deployable entirely through software and without the physical intervention of a system manager. The product consists of a 24x30x84-inch chassis containing 24 two-way and/or four-way SMP processing resources, redundant central controllers, redundant integrated switches, redundant high-speed interconnects and Egenera PAN Manager software. 

In another development, Switch Computing Architecture, as popularized by TopSpin Communications, provides unified switched fabric for IPC, Fibre Channel, and Ethernet for interconnecting computing elements into server area networks. This would enable the creation of virtual computers from pools of industry-standard processors, storage, and I/O building blocks. It improves performance in three parts of the network, namely host-to-host interconnect communications, host-to-LAN/WAN communications, and host-to-storage communications. Terabits of aggregate bandwidth in a single chassis, and Sub-10 microsecond latencies within the switches help in setting up high performance clusters.

The new and evolving architectures, specifically Process Area Networks (PAN) and Server Area Networks, are helping to create and manage powerful clusters.