[Simh] VMS versions with LAVC support

[Paul Koning]

> On Mar 11, 2017, at 10:57 AM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> On 2017-03-11 16:37, Timothy Stark wrote:
>> 
>> Well, I learned that oldest VMS that support  LAVC is 5.5-H2.  Oldest VMS version support VAXcluster is 4.0. For 4.0 to 5.5, can it handle DECnet as cluster? More one thing, is that possibly CI-to-Ethernet bridge adapter for older VMS software?
> 
> Not sure what you mean by "handle DECnet as cluster".
> But before LAVC, the only way to cluster was over CI, which simh do not emulate. So, if you want any kind of cluster, you *have* to do it over ethernet, which means you need at minimum VMS V5.5-H2.
> 
> There is no CI to Ethernet adapter. It is two different network technologies, with no easy translation between them.

Exactly.  CI is a closed network, not interconnected to anything else, not related protocol-wise to anything else.  LAVC is a way to provide the same data services over a rather different network, namely Ethernet.

One interesting point is that the CI protocol (SCA) is an RDMA protocol.  I'm not sure if it is the very earliest but it certainly predates widespread adoption of that notion (or that terminology) by several decades.  Note that LAVC does not do RDMA; that plus the lower speed of Ethernet at the time (10 Mb/s) is why LAVC was viewed originally as a low end clustering technology -- suitable for workstations but not as a CI alternative for full size VAXen.

	paul