ARPANET IMP (Interface Message Processor) Port Expander.

摘要

The ARPANET was originally conceived to support high-data-rate distant communication between large mainframe computers. Because of the hardware limitations of the Honeywell 316/516 processor, which was selected as the original ARPANET interface processor (IMP), most ARPANET IMPs are restricted to supporting a maximum of four host attachments (computers or gateways to other networks). As the ARPANET community expanded many sites experienced the need for more than four host ports. The response was to install additional IMPs. With the H316/516 no longer available and the C/30 IMP, being developed by the BBN Computer Company not expected to arrive until 1981, no more ARPANET nodes/host ports were available. Simultaneously with this growth in the ARPANET community, hosts attached to IMPs have increasingly tended toward less powerful types, such as the DEC PDP-11 minicomputer. Many of these minicomputer hosts require only moderate data-rate network communication or occasional access. The desire to attach a large number of minicomputers or microcomputers to the ARPANET induced DARPA to assign SRI the task of developing the port expander concept into a working product. This manual describes the functions, installation, and operation of the port expander.