[TUHS] off-topic: resurrecting the IMP

Aharon Robbins arnold at skeeve.com
Mon Dec 2 07:18:26 AEST 2013

Hi all.

This may be of some interest.  From a friend at Utah:

> 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.


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