VMS stability back in the day (was Re: NuTek Mac comes)

Paul Koning paulkoning at comcast.net
Fri Jul 15 09:31:30 CDT 2016

> On Jul 15, 2016, at 10:08 AM, Mouse <mouse at Rodents-Montreal.ORG> wrote:
>> DECnet might be totally integrated and awesome, but it's also
>> proprietary, seldom used,
> ...
> However, IIRC it also has a fairly small hard limit on the number of
> hosts it supports.  I don't remember exactly what the limit is;
> different memories are handing me 10, 12, and 16 bits as the address
> size, but even the highest of those is sufficient for at most a large
> corporation.  (Maybe it was 6 bits of area number and 10 bits of host
> number within each area?  I'm sure someone here knows.)

Correct.  16 bits total in Phase IV (up from 8 bits in Phase II and III).

Then again, with NAT ("hidden areas") that worked acceptably well even for the largest DECNet (the one at Digital).  Keep in mind that DECnet was designed as a network for an organization, not as an internet.

> Perhaps if DEC had enlarged the address space (somewhat a la the
> IPv4->IPv6 change) and released open-source implementations, it might
> have been a contender.  For all I know maybe they've even done that,
> but now it's much too late to seriously challenge IP's hegemony.

DECnet did increase the address space, with Phase V where the address is variable length up to 20 bytes.  The difficulty is that it was all based on OSI, with all the international standards bureaucracy that implied.  And by that time, TCP/IP had become a viable competitor, which was "good enough" (32 bit addresses) and sufficiently much simpler and more nimble that it came out the winner.

> But the real shining star of DECnet/VMS was not the protocols, but the
> ground-up integration into the OS.

Well said.


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