[Discuss] Whence distributed operating systems?

[bogstad at pobox.com (Bill Bogstad)]

On Sun, Apr 24, 2016 at 10:35 AM, Rich Pieri <richard.pieri at gmail.com> wrote:
> nb: I received this Sunday morning. Not sure where the delay was.
>
> On 4/21/2016 10:14 AM, Jack Coats wrote:
>> In many ways, we do have a single system signon, with a 'single system
>> image' for well developed systems today.
>
> That's not single system image, though, even if it presents the
> illusion. Lemme give you a concrete example, one of the last serious
> attempts at practical, commercial SSI that I'm aware of: Digital's
> Galaxy architecture.
>
> Galaxy was an evolution of VAX/VMS clustering. The idea was to be able
> to construct arbitrarily large VAX clusters from what they called quad
> building blocks or QBBs. Each QBB was 4 Alpha CPUs and 2GB RAM (IIRC)
> and was plugged into a fast fibrecchannel backplane. The prototype I saw
> in Nashua was a 4 QBB system.
>
> Galaxy had two configurations. The first was a traditional VAX cluster
> with each QBB operating as a single node, so the prototype was a 4 node
> cluster with 4 processors and 2GB RAM each. Traditional VAX clusters are
> sometimes seen as partial SSI due to the cluster-aware file system (one
> of the first ever) and live process migration capabilities (again one of
> the first ever).

This is in fact what I think of when I hear the term SSI.   In the
Unix/Linux world,
there was Locus (and IBM's AIX for 370 & PS/2s).  You could even have both
370s and PS/2s in the same SSI.  Obviously processes couldn't migrate between
them, but otherwise they were treated the same. I worked with this system a bit
many years ago.  There is also Mosix which I believe may still be around and had
a Linux based version.   No experience with this

> The second was the namesake galaxy configuration. All of the QBBs were
> glommed together into a single large computer. In this configuration,
> processes on the prototype saw 1 processor with 16 streams and 8 GB RAM
> rather than a 4-node cluster. A processes could allocate more than one
> QBB's worth of RAM and not hit swap. It could have threads running on
> any or all of the QBBs without having to be programmed specifically for
> it. Galaxy was full SSI.

So memory was shared? between the QBBs?   This sounds more like a NUMA
architecture environment.  What would you say are the differences
between this definition
of SSI and NUMA?

Bill Bogstad