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2 Local Area Networks     continued...

The second category of machines on a network are servers. As their name suggests, these nodes provide services to other nodes and are shared by many users. Printers are a good example: rather than connect a printer directly to one computer, and forcing each person to use that computer in order to print a document, a printer with a built-in network interface can be connected directly to the network and used by any system. Other common types of servers are file servers and compute servers. A file server is often just a workstation with extra disk space, but most workstation manufacturers build special server configurations for higher performance and better reliability. Mainframes and supercomputers that are likely to be used by computational scientists are usually compute servers on a local network. The term ``compute server'' reflects the fact that mundane jobs like editing files and reading mail are done on workstations and microcomputers, but users can run computationally intense jobs on these special purpose high performance systems.

The third category of network equipment is an interface to another network. These interfaces are either gateways or routers. A gateway translates information between the formats used by two different types of networks. In the early days of local area networking there were few standards and a wide variety of performance levels, and thus different protocols and services evolved in different settings. For example Apple microcomputers could be connected via an Appletalk network. If these machines were to be linked to a set of Unix machines, one of the Unix systems typically ran a software package that translated Appletalk protocol packets into the format used by the Unix systems.