Top 500 trends

Richard Walsh rbw at ahpcrc.org
Wed Nov 27 16:28:09 EST 2002


On 27 Nov 2002, Robert Brown wrote:

>On still other sides, "supercomputers are clusters".
>
>We should probably differentiate between vector supercomputers (Greg's
>point, which is well taken) and e.g. SP supercomputers, which are
>basically clusters.  Really expensive clusters, but clusters.

 This IS an important point ... in that Power 4 clusters even with
 one core turned off do not compete with vector machines or even the
 Alpha or the best P4 nodes on a stream bandwidth basis. So as "really
 expensive clusters" as Robert puts it, what is the extra money going
 for ... I guess excellent in-cache peformance, 64-address space,
 some operating system niceties perhaps, and IBM's support/service 
 to a captured/installed market.  There may be other items that I am
 missing here, but most of these features can be had elsewhere for
 a substantial discount ... they are just not Big or Blue.

 On the other hand, the X1 and SX5/6 machines offer the still-unique 
 (but shrinking) per CPU bandwidth capability of the vector architecture 
 (now combined in systems that scale to 1000s of processors).  The price 
 is high, but such a 1000+ processor, vector system (especially with 
 its BMM hardware) is the right choice for customers with ready supplies 
 of your tax dollars ( ;-) ). 

 They can even trump the bandwidth of the large cluster Mark was refering
 to on an absolute performance basis.  The question for the buyer is, "Can 
 I shrink my code's foot print inside the cheap-cluster node's ever increasing 
 cache and if so, do I have more time/talent on my hands or money."  If the
 answer is more money, then buy the "vector cluster". 

 There are a couple less dominant points like SSI, administrative costs, 
 percent utilization, and sustaining the capacity to design custom processor
 /system in the US ... where the custom engineered vector system may also 
 have an edge.

 rbw

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