3.4.4 Memory HierarchyL1 and L2 Caches

		hundred dollars. Towers provide uniform configuration, standardized interface cabling, effective cooling, and a structurally robust component mounting framework but are flexible enough to support a variety of internal node configurations. Industrial grade shelving, usually of steel framework and particle board shelves is strong, readily available, easily assembled, and inexpensive. It is also flexible, extensible, and easily reconfigured. You can find it at your nearest home and garden center.

		When assembling such a system, care should be taken to design tidy power distribution and networking wire runs. Extension cords and power strips work fine, but you should consider physically attaching them to the shelving with screws or wire-ties so that the system does not become an unmaintainable mess. Similar considerations apply to the Ethernet cables. Labelling cables so the ends can be identified without laboriously tracing the entire run can save hours of headache.

		Different approaches are possible for video and keyboard cables. In our systems, most nodes do not have dedicated keyboard and video cables. Instead, we manually attach cables to nodes in the very rare circumstances when necessary maintenance cannot be carried out remotely. Linux's powerful networking capabilities makes it unnecessary to maintain constant console video and keyboard access to each and every node of the system.

		Rack mounting is considerably more expensive but offers the possibility of much higher physical densities. New motherboards with rack mountable form factors that incorporate Fast Ethernet controller, SCSI controller and video controller offer the possibility of building Beowulf nodes that can be packaged very tightly because they don't require additional daughter cards. It is likely that these systems will be important in the future, as larger Beowulf systems are deployed and machine room space becomes a major consideration.

		3.10 Node Assembly

		We conclude this section with a checklist for building a Beowulf node. Building Beowulf nodes from component parts may not be the right choice for everyone. Some will feel more comfortable with systems purchased from a system integrator, or they simply won't have the manpower or space for in-house assembly. Nevertheless, one should not overlook the cost, which can be several hundred dollars per node and carefully weigh the luxury of having someone else wield the screwdriver vs. owning 25% more computer power. Keep in mind that cables often come loose in shipping, and there is no guarantee that the pre-assembled system will not require as much or more on-site trouble-shooting as the home-made system.