The IUMSC Beowulf cluster consists of nine dual-CPU Compaq Proliant ML370 systems connected together by a dedicated, switched fast ethernet / gibabit ethernet network.  Switching duties are handled by an HP Procurve 4000M switch equipped with five 10/100-base TX modules and one gigabit module.  One Proliant serves as the master node -- it alone is connected to the external network, and it handles all interaction with the outside world, including receiving job submissions, serving logins, and keeping logs -- the remaining systems are dedicated to computation as directed by the master.  The master node has two gigabit ethernet interfaces, one for the external network and one for the internal, whereas the other nodes use fast ethernet interfaces to the internal network only.

Rendering job submission and response are accomplished via custom client and server programs.  The actual ray tracing is performed by a modified version of the distributed ART (Another Ray Tracer) program from the somewhat venerable but highly functional VORT (Very Ordinary Rendering Toolkit) package.  The images produced elsewhere in this demonstration are fixed at 600x600 pixels, but any image size up to 4096x4096 pixels can be requested through the rendering client, and even that is an arbitrary limit.  Rendering time for any particular model does scale with the number of pixels, of course.  The cluster is not limited to drawing molecules, either -- that is a limitation of the interfaces.  The rendering client can deliver any VORT-format scene description to the cluster, which doesn't know or care whether the scene describes a molecule.