2.4 A Critical Technology Convergence

		2.5 The Beowulf System Node

		As in all clustered systems, the fundamental building block is casually referred to as a "node" which is a stand alone computing system with complete hardware and operating system support to fully manage the execution of a user program and interact with other nodes over a network. Nodes of a cluster can be as small as a desktop system costing on the order of a thousand dollars or a mighty multiprocessor SMP costing millions of dollars. For a Beowulf cluster system, the node is usually a personal computer derived from the commercial mass market exhibiting an excellent price/performance ratio. This does not necessary imply the absolute lowest price system but rather the optimal balance of capability and cost, for the problem at hand.

		A Beowulf hardware node incorporates a number of subsystems, each providing the Beowulf system integrator with multiple choices. These provide processing capability, information storage, and external I/O. System area networking will be described as a separate topic.

		Processor

		There are three principal families of microprocessors that are incorporated into personal computers and sold at low cost to the general public. The Intel x86 family is employed primarily in PCs with Microsoft MS-DOS, Windows, and NT operating systems; the IBM/Motorola PowerPC family is employed primarily in the Apple Macintosh computers to run the MacOS operating system; and the DEC Alpha family is available in PC style packaging and most often runs NT or Digital Unix. The Linux operating system has been ported to all three processor families (and several others). Intel processors are most widely used for Beowulf-class computing but Alphas have found a niche where floating point intensive computations are involved. All three families incorporate advanced memory management including caches, virtual memory and address translation. The choices facing the Beowulf designer includes:

		processor family,

		clock rate of processor

		cache size associated with processor

		Motherboard

		Motherboards are far more than a convenient surface onto which the chips are glued. They contain complex logic in their own right and can have significant effect on the