2.5 The Beowulf System Node

		Floppy Drive

		A portable 1.4 MByte storage device with form factor of 3.5" was once the dominant means of transferring code between systems. Now it is still used to some degree, but with the advent of the inexpensive CD-ROM and the availability of the Internet, it is losing preeminence as the favorite transfer medium. Floppy drives cost less than $20 and are crucial for initial system installation and crash recovery. One should be installed on every node.

		Support Devices

		Some additional devices are included on one or more nodes to facilitate certain types of servicing or monitoring operations. Among those are the following:

		External Local Area Network Beowulfs always exist within an infrastructure that provides broad user support and access. Connection to this environment is provided through one or more network interface cards (NICs) attached to the local area network. One or more of the nodes in a Beowulf system have such cards and IP addresses that allow external access. The type of NIC is chosen to be compatible with the LAN environment.

		CD-ROM Drive  CD-ROM is an optical storage medium, 5.25 inches in diameter capable of storing about 650 MBytes. Drives cost well under $100 and can spin at up to 24 times the speed of the equivalent drives used to play music CDs. CDROMs have become the principal medium for the distribution of large software packages. For example, Linux is available from multiple sources on CD-ROM. One drive should be sufficient for an entire Beowulf system.

		Monitor/Keyboard While not necessary, most Beowulfs have a direct user interface. One of the nodes is used as a host or user node with monitor, keyboard, and mouse interfaces. This node is employed primarily for system administration, diagnostics, and statistics presentation. It may also used as a high bandwidth graphical port for data visualization.

		2.6 The Beowulf Network

		Second only to the node itself, the internal system area network is the most important subsystem of a Beowulf cluster both in terms of achieving sustained performance and contributing to cost. Beowulfs often (but not always) employ the Ethernet and TCP/IP protocols developed and marketed for local area networks.