4.9 Keeping Up with Linux

		II clock rates are more than double that and DEC Alpha processors operate at 533MHz and higher. The PCI bus will soon support a data path twice as wide and twice the clock rate, permitting high bandwidth data transfers to peripheral devices including Gigabit NICs. A broader range of Beowulf applications can be effectively supported with higher bandwidth. The experience with Fast Ethernet demonstrated that a rapid and dramatic drop in price can be expected once the technology is adopted by the mass-market. The 1 Gbps technology is in place and experience by manufacturers is leading to rapid improvements and cost cutting. Some Beowulf installations have already experimented with Gigabit Ethernet and the Beowulf project has already delivered drivers to the Linux operating system for several Gigabit Ethernet cards.

		5.2 Alternative Network Technologies

		In spite of its popular use in existing Beowulfs, Ethernet-based networking is not the only technology choice for enabling inter-node communication. Other solutions exist that can deliver equal or better performance depending on the application. Fast Ethernet is a popular choice because of its ubiquity and consequent low price. A Fast Ethernet card costs only about 2% of the price of today's $1,000 Beowulf nodes. Only the network switches have a significant impact on the overall price of the system. With other networking technologies, each network interface card can cost as much as a 16-port Fast Ethernet switch. So you have to think carefully before committing to an alternative network. If the kinds of applications you intend to run require specific properties, such as low latency, which are not provided by Fast Ethernet, then it is likely worth the additional cost. For example, real-time image processing, parallel video streaming, and real-time transaction processing all require low latencies and do not work well with Fast Ethernet. We will briefly discuss the most common alternative networking technologies used by Beowulf systems. Not enough data has been collected on application performance in systems using these technologies for us to comment on when each should be used.

		5.2.1 Asynchronous Transfer Mode

		Asynchronous Transfer Mode (ATM) is a networking technology developed primarily by the telecommunications industry in order to consolidate both their data and voice networks. ATM is intended to support isochronous guaranteed-bandwidth data streams typical of communication channels, with the irregular traffic of typical computer applications supported only as a simple subset of the functionality.