Talk:IMP interface

DR11C

Re DR11C. I peeked at the driver in 2.11BSD and I think it said Unibus. But it was only a brief glance. Larsbrinkhoff (talk) 10:11, 15 March 2018 (CET)

Hey, this mentions UNIBUS:

• https://www.retro11.de/ouxr/43bsd/usr/man/cat4/css.0.html

Larsbrinkhoff (talk) 10:19, 15 March 2018 (CET)

Huh? That page talks about the IMP11-A, the DEC CSS thing.

Anyway, for the SRI thing, it was possibly both, actually. What it was was an SRI board that took the bit-stream from the IMP, doing the host-IMP harware protocol ('there's your bit', etc), and converted it to words, which it shipped over a parallel interface to a standard DEC DRV11 card. I'm pretty sure the QBUS DRV11 and UNIBUS DRV11-C had the same parallel port spec, so you could probably have plugged the SRI card into a DR11-C instead of a DRV11. Since the DR11-C/DRV11 are programmed I/O, they wouldn't have had the performance of the others, which were DMA, which is probably why UNIBUS machines tended to go with the DEC/ACC interfaces. Jnc (talk) 15:55, 15 March 2018 (CET)

Sorry, wrong link. This is better:

• https://www.retro11.de/ouxr/211bsd/usr/man/cat4/sri.0.html

Yes, I see now DR11-C is the name of a parallel interface. The BSD drivers use the Unibus device to talk to the IMP interface.

Here's a manual for the IMP interface:

• http://www.dtic.mil/dtic/tr/fulltext/u2/a037212.pdf

Larsbrinkhoff (talk) 08:36, 16 March 2018 (CET)

Right. And here is the 2.11 driver:

• http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.11BSD/sys/pdpif/if_sri.h
• http://minnie.tuhs.org/cgi-bin/utree.pl?file=2.11BSD/sys/pdpif/if_sri.c

Looking at the driver, I'm not sure I understand how it works; it looks like it might loop in the interrupt handler, reading the entire packet? Eh, not important.

Somewhere I have MOS operating system drivers for it.

Also my memory was a bit off - it was byte at a time, not word at a time. Jnc (talk) 15:14, 16 March 2018 (CET)

Dynamic Modeling

MIT-DMS wasn't a typo. Although the situation is confused with many different names over the years (DMCG is another prominent one), I believe the official ARPANET name was MIT-DMS.

Here's a line from a 1980 MIT hosts list:

HOST MIT-DMS,           1/6,SERVER,ITS,PDP10,[DM,MITDM,MIT-DM,DMS]

So MIT-DM and plain DM were acceptable aliases. Other lists, e.g. https://github.com/ttkzw/hosts.txt, only says MIT-DMS with no aliases. Larsbrinkhoff (talk) 05:32, 21 October 2021 (CET)

We always called it plain 'DM', and a lot of software called it that, too - e.g. MLDEV. (IIRC, there was a directory which held binary for loadable devices, so when you referenced 'XXX:AAA; BBB CCC' it went and looked there for the correct file for XXX - the filename format and directory escape me at the moment - but you could look at a dump and see if there's a 'DMS' entry there, as well as 'DM'; they were actual files, so the dump would have captured them.) So that's why I changed it (my only goal is maximum accuracy), but I don't have any major commitment to using 'DM'; if you feel that 'DMS' is more accurate, feel free to change it back. Jnc (talk) 13:22, 21 October 2021 (CEST)

The file names for loadable devices are "DEVICE;JOBDEV xxx" where 'xxx' is the device name.

But while looking for that, in SYSDOC;ITS RECENT I found this:

Date: Fri, 28 Mar 86 09:02:47 EST

From: Alan Bawden

All kind of worms are crawling out of the woodwork because of various programs that -know- that all ITS machines are named "AI", "MC", "ML", or "DM".

which matches my memory (above). Jnc (talk) 16:41, 21 October 2021 (CEST)

Yes without a doubt the software on ITS called it DM. It was my intent to use the ARPANET name, as used in the official host lists. But reviewing the article, it's not so important in this context.

More interfaces

Two more interfaces: one for ANTS, and one made at ISI. Stephen Casner wrote: My first work at ISI as a grad student was to help with the hardware debugging of the newly built ISI IMP Interface, a variant of the ANTS Imp Interface from Illinois. At the end of EPOS deployment the aforementioned 11/44 had interfaces to the ARPAnet and the Wideband Satellite Network that were implmented in UMC-Z80 add-in devices developed by Lincoln Lab.

This also hints at the story that ANTS was made so Illinois researchers could access Illiac IV. Larsbrinkhoff (talk) 07:11, 28 October 2021 (CEST)

Yeah, I saw that the ANTS guys did a (UNIBUS) 1822 interface. I didn't try to find any information on it. I wonder how (if at all) it relates to the IMP11-A interface from DEC? That must not have been around when the ANTS interface was done (otherwise why do to the work). I'm trying to remember who used the IMP11-A - ISTR that BBN had a number of them. (And if I get really ambitious, I'll get my scanner machine working again; I should scan my IMP11-A manual, and put it online.) The UIUC UNIX NCP code and the BBN UNIX V6 should show which 1822 interfaces those used.

Also, in the MOS-related investigations, it turned out that SRI co-developed with ACC a DMA 1822 interface. Whether QBUS or UNIBUS I don't recall - maybe first one, and then the other. (The earlier Stanford/SRI interface that used the DR11/DRV11 was interrupt per character, so not good for high-volume applications like the Port Expander - the later Port Expander product used the ACC interface). I have a couple of ACC 1822 manuals here, I should look at them and write up something about those interfaces. (And make sure they are online. Bitsavers has little ACC stuff; the UNIBUS 1822 manual they have seems to have come from me :-). I'll have to look and see if the MIT Gateway used the Stanford or ACC interface; I don't recall. Jnc (talk) 16:08, 28 October 2021 (CEST)