[Beowulf] Confused over the term cluster

[Kozin, I (Igor)]

> Just to be awkward, there are of course machines like the SGI Altix.
> Is it a cluster, or is it a node?  From the programmer's perspective
> it's the latter, from the architectural perspective, the former.
> 
> There's no real dividing line; there are machines across the entire
> spectrum.  But I'm just being difficult, generally I agree with what
> the others have said.

I'd say definitely the former - a cluster where the nodes (two sockets)
are connected using Numalink.

I have been thinking long and hard about those classification issues
when I was designing sufficiently generic but consistent machine
description for our benchmarking database. The view that I took is that
there is a "node" which is a reasonably independent entity and you take
those nodes and glue them together using some sort of "interconnect". So
far this architectural view has not failed me but it is not impossible
that future machines might have more intricate "node" or "interconnect"
structure and therefore require more sophisticated approach.

Programmer's view can't be used for classification purposes because
there can be several views on the same hardware at the same time. The
Altix example is admittedly blurred but even a traditional cluster can
be programmed a la SMP using Cluster OpenMP or other similar approaches
which obviously do not make the underlying hardware any different.

As for the terms processing element (PE) and core, PE was clearly
preferable for machine description rather than core because PE is more
generic whereas the term "core" usually implies a fully functional
processor that has been shrank. Terminologically PE may include
processor cores, SPEs in Cell BE, GPGPUs attached to the node or
accelerating co-processors.