AppleTalk - Physical Implementation

Physical Implementation

Interior of Apple LocalTalk interface box. In 1989, these boxes typically cost US $90 each. The connectors feature automatic electrical termination of the LocalTalk signal bus; insertion of a LocalTalk bus cable depresses a normally closed switch behind the connector, disabling termination for that connector.

The initial default hardware implementation for AppleTalk was a high-speed serial protocol known as LocalTalk that used the Macintosh's built-in RS-422 ports at 230.4 kbit/s. LocalTalk used a splitter box in the RS-422 port to provide an upstream and downstream cable from a single port. The topology was a bus: cables were daisy-chained from each connected machine to the next, up to the maximum of 32 permitted on any LocalTalk segment. The system was slow by today's standards, but at the time the additional cost and complexity of networking on PC machines was such that it was common that Macs were the only networked personal computers in an office. Other larger computers, such as UNIX or VAX workstations, would commonly be networked via Ethernet.

Other physical implementations were also available. One common replacement for LocalTalk was PhoneNet, a 3rd party solution (from a company called Farallon, now called Netopia) that also used the RS-422 port and was indistinguishable from LocalTalk as far as Apple's LocalTalk port drivers were concerned, but ran over the two unused wires in standard four-wire phone cabling. PhoneNet was considerably less expensive to install and maintain. Ethernet and Token Ring was also supported, known as EtherTalk and TokenTalk respectively. EtherTalk in particular gradually became the dominant implementation method for AppleTalk as Ethernet became generally popular in the PC industry throughout the 1990s. Besides AppleTalk and TCP/IP, any Ethernet network could also simultaneously carry other protocols such as DECnet, NetBEUI, and IPX.