The attached link to the Scientific American article on clustering may 
shed some light-
 
http://www.sciam.com/article.cfm?articleID=000E238B-33EC-1C6F-84A9809EC588EF21&pageNumber=2&catID=2


Linux clusters are built cheap to go fast. The article cites a cluster 
built in 1994 for approximately $40,000 that was the functional 
equivalent of a $400,000 supercomputer.  The article also indicates that 
identical pcs are not required to assemble a cluster. The Stone Souper 
Computer discussed in the article ran a hodgepodge  of 486s, Pentiums 
and Alphas on the same cluster.
 
Lee Einer



Liberty Young wrote:

>I was just pondering the following question based on what David said
>earlier today.
>
>>Lots of people would rather spring for a cluster then huge single
>>machine now a days.
>>
>
>
>Putting aside that it's very geek-cool to run or put together a cluster
>of cheap x86 pcs, what are the reasons to have a cluster vs a single
>machine? 
>
>One reason TO have a cluster is that you can run your own clustering OS
>and kernel; then again, the kernel and OS may fall shy of the ones built
>into and for the single machine. 
>
>I was also thinking that with clusters, it is very hard to amass a clone
>army of the same pc for each node. You would HAVE to have a contract
>with a vendor that states very explicitly that they would supply you an
>exact replica for each node. Otherwise, there'd be difficulty  and costs
>involved in maintance. For example, you couldn't just use a single
>restore CD or a ghost image of the machine to install a new one or fix a
>corrupted one. 
>
>Disclaimer: These are just theoritcal thoughts. I'm not a large scale
>administrator of any kind. 
>
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