[ih] PDP11 ARPANET interfaces (was: Arpanet line speed)

[Stephen Casner]

I corroborate Jack's description.  The IMP11a was DEC's implementation
of an interface for a PDP11 to connect to the ARPANET IMP.  Two
predecessor PDP11 interfaces were the ANTS interface from the
University of Illinois and a variant of that design made at USC
Information Sciences Institute.  My first task when I joined ISI in
1973 was to write diagnostic software for it.  All three interfaces
were provided DMA transfer into and out of memory via the UNIBUS.  The
only function you might call processing was an option to swap bytes
going into or out of the 16-bit words of PDP11 memory (since the PDP11
was a little-endian inhabiting a landscape which at that time
consisted of mostly big-endians)

The ISI PDP11 ARPANET Interface is featured in action in the opening
scene of the digital voice converencing movie we made in 1978.

https://www.youtube.com/watch?v=MGat1jRQ_SM

                                                        -- Steve

On Wed, 18 Jan 2017, Jack Haverty wrote:

> That's an IMP interface, which was a peripheral device for the PDP-11
> computers.  One of those was on the PDP-11/40 in a lab at BBN in Fall
> 1977, so it had become a commercial product before then.  It connected
> between an IMP port, following the specifications in BBN 1822, and the
> PDP-11 on the Unibus IIRC.  It didn't do much processing - just
> transferred the ARPANET "messages" to and from the IMP and the computer
> memory.
>
> I wrote the first TCP for Unix, and that's how those IP packets got in
> and out of the machine.  I spent many hours trying to figure out what
> was going on by looking at those lights...
>
> /Jack
>
>
> On 01/18/2017 11:48 AM, Jeremy C. Reed wrote:
> > This got me thinking ... is there any list of where the original IMPs
> > (and modems, etc) are located today? What museums or other places can we
> > visit to see them and learn about them (in person)?
> >
> > On that note, any good museums that have exhibits for the physical
> > history of the internet?
> >
> > Hopefully this list allows my attachment. This is an Digital IMP11a. It
> > is probably around 12 years newer than the original IMPs. I took this
> > photo a few years ago in a Internet Systems Consortium (ISC) warehouse
> > in Redwood City, Calif.