3.1 Overview of a Beowulf Node

		Cache size The storage capacity (KBytes) of the high speed buffer memory between the main memory and the processor.

		Main memory capacity The storage capacity (MBytes) of the primary system node memory in which resides the global data set of the applications as well as myriad other supporting program, buffering, and argument data.

		Disk capacity The storage capacity (GBytes) of the permanent secondary storage internal to the processing node.

		SAN network port peak bandwidth The bandwidth (Mbps) of the network control card and system area network communication channel medium.

		System bisection bandwidth The bandwidth (Gbps) of the choke point in the system area network.

		Other parameters that are sometimes of interest are the number of processors included in symmetric multiprocessing configurations, memory latency and bandwidth, measured performance of various benchmarks, and seek and access times to disks.

		3.1.2 Basic Elements

		The general Beowulf node is a complex organization of multiple subsystems that support the requirements for computation, communication and storage discussed above. Figure 3.1 shows a block diagram of a node architecture representative of the general structures found in today's PCs adapted to the purpose of Beowulf-class computing.

		Microprocessor All of the logic required to perform instruction execution, memory management and address translation, integer and floating point operations, and cache management. Processor clock speeds can be as low as 100 MHz found on previous generation Intel Pentium processors to as high as 533 MHz of the DEC Alpha 21264 with the 400 MHz Pentium II representing near the sweet spot in price/performance.

		Cache Provides the illusion of a much higher-speed memory than is actually available by keeping recently used data in a small but fast buffer. Multiple layers of cache may be employed; 16 KBytes of Level 1 (L1) and 512 KBytes of Level 2 (L2) cache are common. The effect of cache can be dramatic, but not all programs will benefit. Memory systems are so complex that often the only reliable