Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!lll-winken!lll-tis!ames!nrl-cmf!ukma!gatech!hubcap!vrdxhq!ogccse.ogc.edu!pase
From: vrdxhq!ogccse.ogc.edu!pase@uunet.UU.NET (Douglas M. Pase)
Newsgroups: comp.parallel
Subject: Re: Hmm!
Keywords: HyperCube, Parallel Connection Schemes
Message-ID: <3363@hubcap.UUCP>
Date: 27 Oct 88 20:05:09 GMT
Article-I.D.: hubcap.3363
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Approved: parallel@hubcap.clemson.edu

mschedlb@hawk.ulowell.edu (Martin Schedlbauer) writes:
>>  Is the Connection Machiene by ThinkingMachines Inc. a hypercube?
>No it isn't. A hypercube is an architecture, in which nodes are connected to
>their Gray-Code neighbours.

I'm not sure this is correct.  As I recall, there are two networks available
for use in the CM.  The first is a NEWS network (either a torus or a mesh, I
don't remember which), and the second is indeed a hypercube.  One big
difference is that the CM hypercube is synchronous (i.e., a 12-D network
requires 12 steps to transfer data, even if the target is a nearest neighbor).

>Although, the new iPSC/2 uses a message routine scheme called 'wormhole
>principle' where it is almost unimportant who's connected to whom, [...]

Wormhole routing (which should be called wormhole *switching*, as opposed to
circuit or packet switching) does indeed reduce latency on an unloaded
machine.  However, there is still ample opportunity to have communication
hotspots and network saturation because the network topology is really
a hypercube, not a completely connected network (which is anything but flat).
In a completely connected network, saturation can still occur, but hotspots
cannot.  Plus, because of the vast number of links, it takes hard work to
cause saturation in real applications.

>>Is the "new" thing about Hypercubes the way they integrate many many
>>processors, or the whole parallel processing idea?
>The way they connect processors without using expensive crossbar switches and
>still get decent message passing performance.

Another nice thing about hypercubes is that a large number of useful topologies
such as grids, tori, and cubes, are all easily embedded within them.  Another
slick feature is that a number of applications, such as FFTs, matrix ops, and
sorts (ie. bittonic (sp?)) map directly to a hypercube, and thus all links
are used with high efficiency (multihop messages need not occur).
-- 
Douglas M. Pase				Department of Computer Science
tektronix!ogccse!pase			Oregon Graduate Center
pase@cse.ogc.edu (CSNet)		19600 NW Von Neumann Dr.
(503) 690-1121 x7303			Beaverton, OR  97006-1999