Pluribus

The Pluribus[1] multiprocessor was an early multi-processor computer designed by BBN for use as a packet switch in the ARPANET.

The network was growing rapidly in several dimensions: number of nodes, hosts, and terminals; volume of traffic; and geographic coverage (including plans, now realized, for satellite extensions to Europe and Hawaii).

The designers decided on a multiprocessor approach because of its promising potential for modularity, for cost per performance advantages, for reliability, and because the IMP packet switch algorithms were clearly suitable for parallel processing by independent processors.

Custom-built bus couplers connected the bays to one another so that the processors could reach the shared memory and the I/O devices.

A 6-processor Pluribus was used as a network switch to interconnect BBN's five Tenex/"Twenex" timesharing systems along with 378 terminals on direct serial and dial-in modem lines.