Date: Sat, 30 Nov 2013 16:06:25 -0700 (MST) Subject: [it-professionals] computer history: Arpanet IMPs resurrected The simh list about simulators for early computers recently carried traffic about an effort to reconstruct and resurrect the Arpanet Interface Message Processors (IMPs), which were the network boxes that connected hosts on the early Arpanet, which later became the Internet. There is a draft of a paper about the work here: The ARPANET IMP Program: Retrospective and Resurrection http://walden-family.com/bbn/imp-code.pdf Utah was one of the original gang-of-five hosts on the Arpanet, and we received IMP number 4. Utah is mentioned twice in the article, and also appears in the map in Figure 3 on page 14. One amusing remark in the article (bottom of page 7) has to do with the fail-safe design of the IMPs: In addition ``reliability code'' was developed to allow a Pluribus IMP to keep functioning as a packet switch in the face of various bits of its hardware failing, such as a processor or memory [Katsuki78, Walden11 pp. 534-538]. This was so successful there was no simple off switch for the machine; a program had to be run to shut parts of the machine down faster than the machine could ``fix itself'' and keep running. As happened with early Unix releases, machine-readable code for the IMPs was lost, but fortunately, some old listings that turned up recently allowed its laborious reconstruction, verification, assembly, and simulation.