[HECnet] DECnet Implementation and Productization of RSX-11M, 11S, 11D and IAS (was Re: Anonymous FAL (Tops-20))

[Johnny Billquist]

On 2019-07-16 17:50, John Forecast wrote:
> 
> 
>> On Jul 15, 2019, at 7:48 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> On 2019-07-15 17:36, John Forecast wrote:
>>>> On Jul 14, 2019, at 11:55 PM, Thomas DeBellis <tommytimesharing at gmail.com <mailto:tommytimesharing at gmail.com>> wrote:
>>>>
>>> 2. RSX-11M/11S - any PDP-11 system with sufficient memory + devices
>>> Device drivers ran as part of the ‘kernel’ serialized by the fork block mechanism
>>
>> Right. And I/O completion is normally handled by a couple of routines in the kernel, so the driver itself can be pretty minimal.
>>
>>> I guess RSX-11M+ could be consider a separate class adding I/D space, supervisor mode and multi-processor support.
>>
>> Nah. 11M+ is really very similar to 11M. They pretty much share the same codebase, but M+ extends some data structures with a bit more information, and also adds a couple of more structures to make the system more flexible.
>> The splitting of I/D space, as well as supervisor mode actually have very little impact on the kernel. There is obviously a bit more work at a context switch, and there are a couple of details around ASTs, which can switch between user and supervisor, but much of the rest don't know or care. And drivers can pretty much be moved straight over, although you normally would want to modify them to take advantage of some nifty additional capabilities provided by M+.
>>
> There were a lot of small changes throughout the networking code to get it running on our dual-processor. We eventually shipped with the kernel networking code running with cache bypass enabled and the intention of revisiting it in a later release. One the 11/74 was cancelled, we were never given the opportunity…

Ah, yes, I tend to skim over the mP changes, but you are right. DECnet 
is one of those things that got hit because of that, as well as some 
kernel parts. It's still fairly contained. It's just that CEX knows a 
little too much to not get affected. Most device drivers are totally 
unaware of mP aspects.

Interesting that you think you might have improved DECnet with a bit 
more work. As it stands, it works fine today. But I haven't looked into 
how much might be running without cache enabled. But I am running a 
simulated 11/74. That is Mim.Update.UU.SE. You can both browse to it, 
and telnet to it. Usually I only have two CPUs online, since there are 
still some issues with the emulation. But otherwise it works fine.

I also had to figure out some issues with TCP/IP and multiprocessor 
support. That was interesting. :-)

>>>> 1. What is the latest Phase DECnet that 11M will run?  I guess the
>>>>     last release was 93?
>>> Phase IV. The last release I see on bitsavers.org <http://bitsaver.org> was 4.5 in Oct 1989
>>
>> No. Last/latest release was in 1998/1999 (depends on whether you look at 11M or 11M+). But it was still all just phase IV.
>>
> That must be a Mentec release? I was long gone from DEC at that point in time.

Yes. Mentec released both 4.5 and 4.6 of M+. The last DEC release was 
V4.4, in 1993 or 1994. Right before it was sold off to Mentec.
(Corresponding 11M was 4.7 and 4.8, with the last DEC release being 4.6.)

>> Latest 11M is V4.8, and latest 11M+ is V4.6.
>> I think they are even available to trailing-edge…
>>
> That’s the base 11M/11M+ distribution? Do you know if there was a corresponding DECnet release?

The M+ 4.6 disk image at trailing-edge actually contains the DECnet code 
as well. And yes, DECnet-11M-PLUS V4.5 and V4.6 was released in parallel 
with RSX-11M-PLUS V4.5 and V4.6.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol