[ih] First ARPANET Link Put Into Service: November 21, 1969
Steve Crocker
steve at shinkuro.com
Sun Nov 23 17:17:15 PST 2025
Jack,
Interesting. I interviewed Ben and heard some of details. I reply more
fully when I have time.
Steve
Sent by a Verified
sender
On Sun, Nov 23, 2025 at 8:13 PM Jack Haverty <jack at 3kitty.org> wrote:
> Steve,
>
> You might be interested in the behind-the-scenes story. When I was
> working on a patent fight in 2012, Ben reminisced about IMP1:
>
> "You spoke of how tight the IMP code was. Do remember that the entire
> thing, buffers, data structures, and all, fit in 12k 16-bit words. I
> shudder to think.
>
> Just before we were to ship IMP 1, we had a problem where the machines
> would crash mysteriously about once per 24 hours. It was a weird crash,
> with the PC pointing at a completely random place, typically in a chain of
> non-executable locations in a data structure, with no way it could have
> gotten there. The location before would have caused a crash, there were no
> jumps to it (with or without indexing ior indirection). I concluded that it
> had to be a race condition with the heavy use of the DMC channel. I went
> through the Honeywell drawings of the 516 processor and found a place where
> the timing looked too tight. I figured a way to patch it in the
> processor. I rewired it less than 24 hours before scheduled ship. It
> fixed the problem and the machine shipped on schedule. We had a heck of a
> time convincing Honeywell that they had this fundamental design flaw in the
> central timing chain of their machine, but they eventually were convinced
> and made the change in their future machines."
> Ben did a lot of the work involved in actually getting IMPs to work in the
> field. Most of that has probably never been publicized, being not as
> interesting as things like routing algorithms. But when we were tasked by
> Vint to "make the Internet into a 24x7 operational service", the ARPANET
> guys were just down the hall operating the ARPANET so it was easy to do
> technology transfer to the Internet.
>
> Ben was a hardware guy and a "doer"; here's another of his recollections
> about the "reload from neighbor" capability:
>
> "I wrote a lot of 316 code. As you say, it was pretty easy after writing
> lots of assembler code for the PDP-1, PDP-8, PDP-10, and a bunch of others.
> I wrote all the IMP diagnostics that I used in checking out all the
> interfaces. (Did you know that the 516 IMPs were shipped with an optical
> paper tape reader that was automatically activated by the Watch Dog Timer?
> With a big old relay that would power the PTR up?) That was a pain,
> particularly given that the paper tape had to be picked up off the floor
> and rolled up again. There were 3 copies of the whole program on the tape,
> but after 3 tries, you were done. And the tape would get misplaced by site
> personnel. I figured out the trick of setting up a machine to do a Modem n
> input over all memory and setting up its neighbor to do the output from all
> memory as a MUCH better way to reload the IMP. And you didn’t have to send
> out new paper tapes to all the sites and get someone to mount them every
> time you did a patch."
>
> So you can blame Ben for getting IMP1 onsite, working, early, and
> destroying your grace period. I've learned that researchers rarely think
> about operational issues, and the people who get it running have to fill in
> the gaps - even if it means fixing someone else's design flaw or mitigating
> the effects of onsite conditions.
>
> Enjoy the history!
>
> /Jack
>
> On 11/23/25 15:30, Steve Crocker wrote:
>
> Jack,
>
> BBN was having hardware trouble as the time neared for the delivery of the
> first IMP. I was relieved because we were running late with our software
> to talk to the IMP. I figured the IMP would arrive and then a Honeywell
> technician would show, followed sometime later by a BBN person to check it
> out. I figured I had at least two weeks grace. No such luck. They fixed
> hardware glitch, put the IMP on a plane and delivered it two daysa EARLY.
> Worse yet, they plugged it and it worked immediately :)
>
> Steve
>
> Sent from my iPhone
>
> On Nov 23, 2025, at 6:16 PM, Vint Cerf <vint at google.com> <vint at google.com>
> wrote:
>
>
> I made heavy use of the fake hosts for generating traffic, absorbing
> traffic, reflecting traffic (ping) and for tracing paths taken by packets.
>
> v
>
>
> On Sun, Nov 23, 2025 at 5:51 PM Jack Haverty via Internet-history <
> internet-history at elists.isoc.org> wrote:
>
>> There was a process involved in adding an IMP to the ARPANET. It no
>> doubt changed over time, so what happened with IMP #1 and #2 may be
>> different. I tried asking Ben Barker, since he is mentioned in that
>> 1969 log entry, but the email addresses I have sadly no longer work.
>>
>> IMPs had "fake hosts" which acted like real hosts but were implemented
>> as software inside the IMP. Back in 2012, Ben was helping with the
>> resurrection of the old IMP code and told me:
>>
>> "The IMP code supported a number of "fake hosts". The TTY was one. DDT
>> was
>> another. There may have been another 1 or 2; I had no use for them if
>> they
>> existed, and do not remember them.
>>
>> Each IMP had a hardware card that contained its IMP number, I believe.
>>
>> There was a bit in the header that specified whether the message was for a
>> real host or a fake host.
>>
>> I believe that the TTY was fake host 1 and the DDT was fake host zero.
>>
>> I believe that the default was that the TTY would be set to connect to the
>> same IMP's DDT."
>>
>>
>> Part of the process of getting an IMP online was to first get the two
>> IMPs talking to each other. The TTY on one IMP could connect to the TTY
>> on the other IMP, so the engineers at the two sites could "talk" over
>> the net. You could also connect to the remote IMP's debugger (DDT) and
>> examine or modify the remote machine's memory.
>>
>> After all that connectivity was working and the IMPs were judged
>> functional, then the actual physical hosts could test their ability to
>> communicate.
>>
>> So it's possible that the fuzziness in the timeline was because it may
>> have taken a few weeks to run tests, get all the bugs out, and then
>> declare the first 2 nodes of the ARPANET, and the NCPs in their attached
>> hosts, to be "in service". The stories I've heard recounted that the
>> initial testing crashed with only the LO part of LOGIN successful.
>>
>> One of the other fake hosts in the early IMPs was the one that sent
>> measurement data to UCLA. More than a decade later, when we were
>> involved in getting TCP/IP deployed, we noticed that the UCLA fake host
>> was still in the code. So we used it to create a "Remote Datascope" for
>> DDN (of course, worked in other ARPANET clones too) that could capture
>> the TCP and IP headers of host-host traffic -- invaluable for figuring
>> out what TCP was doing, especially as newly-written implementations by
>> big government contractors were coming online.
>>
>> I doubt anyone knew, in 1969, what was starting then and how important
>> it would be.
>>
>> /Jack
>>
>> On 11/23/25 13:04, Steve Crocker wrote:
>> > After seeing the back and forth on this thread, I now think 21 Nov 1969
>> was when Larry Roberts came to UCLA. I'll try to check with Kleinrock.
>> >
>> > Steve
>> >
>> > Sent from my iPhone
>> >
>> >> On Nov 23, 2025, at 3:48 PM, Jack Haverty via Internet-history <
>> internet-history at elists.isoc.org> wrote:
>> >>
>> >> Perhaps someone in the Bay Area can go to CHM and ask what actually
>> happened on November 21, 1969...? /Jack
>> >>
>> >>> On 11/23/25 12:22, Barbara Denny via Internet-history wrote:
>> >>> Here is Don Nielson's response to my inquiry. I did cut out the
>> first paragraph as it only was for me. There is a typo regarding the 1972
>> ICC meeting.
>> >>> barbara
>> >>> ----- Forwarded Message ----- From: Don Nielson <
>> nielsonz at pacbell.net>To: Barbara Denny <b_a_denny at yahoo.com>Sent:
>> Friday, November 21, 2025 at 10:05:40 PM PSTSubject: Re: Fw: [ih] First
>> ARPANET Link Put Into Service: November 21, 1969
>> >>> "*** paragraph deleted*****
>> >>> I'm certain about the following:
>> >>> 1. First ARPANET connection - Between Bill Duvall at SRI and
>> Charlie Kline of UCLA
>> >>> on what has been accepted as 29 Oct 1969. I tried my best to
>> confirm the date
>> >>> while this date was being pushed by Len Kleinrock of UCLA. Even
>> I and Marc Weber
>> >>> the CHM dug into Engelbart's dinky handwritten notebooks and
>> other stuff on file at
>> >>> Stanford. As far as we could tell, nothing was noted on the SRI
>> end, indicating no big
>> >>> deal at the time. So, what has come to be accepted derives
>> from a brief jot on Charlie's
>> >>> scratchpad: "22:30 Talked to SRI Host to Host". Charlie and
>> Bill are still around
>> >>> and have confirmed and elaborated on the incident, being quoted
>> in some places.
>> >>> 2. ARPANET demo at the International Computer Communication
>> Conference in WDC
>> >>> of NCP in Oct 19723.
>> >>> 3. First 2-net demo of TCP was on 27 Aug 1976. PRNET and ARPANET.
>> >>> 4. First 3-net demo of TCP was on 22 Nov 1977. PRNET, SATNET, and
>> ARPANET.
>> >>> All this is easily available so 21 Nov 1969 seems an aberration
>> by someone.
>> >>> Take good care, Don
>> >>> On 11/21/25 10:14 AM, Barbara Denny wrote:
>> >>> Hi Don
>> >>> Hope you are doing well. This came up on the internet history
>> list. I am wondering if you could shed some insight on the log.
>> >>> Hope you have a good holiday.
>> >>> barbara
>> >>> ----- Forwarded Message ----- From: Vint Cerf via
>> Internet-history <internet-history at elists.isoc.org> To: Jack Haverty <
>> jack at 3kitty.org> Cc: "internet-history at elists.isoc.org" <
>> internet-history at elists.isoc.org> Sent: Friday, November 21, 2025 at
>> 09:50:33 AM PST Subject: Re: [ih] First ARPANET Link Put Into Service:
>> November 21, 1969
>> >>> crocker and I were wondering the same thing off the list.
>> >>> v
>> >>> On Fri, Nov 21, 2025 at 12:49 PM Jack Haverty via
>> Internet-history <
>> >>> internet-history at elists.isoc.org> wrote:
>> >>> > Can anyone explain why the article says "What Happened on
>> November 21st"
>> >>> > but the image of the "First ARPANET IMP log" shows "29 OCT"? /Jack
>> >>> >
>> >>> > On 11/21/25 09:37, vinton cerf via Internet-history wrote:
>> >>> > > there are so many milestone dates....
>> >>> > >
>> >>> > > v
>> >>> > >
>> >>> > >
>> >>> > >
>> >>> > > On Fri, Nov 21, 2025 at 12:03 PM Frantisek Borsik via
>> Internet-history <
>> >>> > > internet-history at elists.isoc.org> wrote:
>> >>> > >
>> >>> > >> Happy birthday to the Internet!
>> >>> > >>
>> >>> > >> https://www.computerhistory.org/tdih/november/21/
>> >>> > >>
>> >>> > >> All the best,
>> >>> > >>
>> >>> > >> Frank
>> >>> > >>
>> >>> > >> Frantisek (Frank) Borsik
>> >>> > >>
>> >>> > >>
>> >>> > >> *In loving memory of Dave Täht: *1965-2025
>> >>> > >>
>> >>> > >> https://libreqos.io/2025/04/01/in-loving-memory-of-dave/
>> >>>
>> >>>
>> >> --
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