Originally posted by: halfadder
Itanium2 is a great CPU for "big data" number crunching, as are the custom CPUs found in Cray's X1. These sorts of machines often have dozens or even hunderds of CPUs per system (not a cluster). The downside is they're harder to program for. Because of the funky VLIW design of the Itanium2, it's hard to debug at the assembly level and most of the performance boosts come via careful data packing and heavy use of Intel's compiler optimizations.
SGI sells a line of machines called the Altix:
http://www.sgi.com/products/servers/altix/
They run SuSE Linux and can handle 512 CPUs per system (1024 and 2048 CPUs with an experimental kernel). NASA has a 10,240 processor Altix cluster, it's actually 20 altix systems, each with 512 CPUs.
Sun still makes good equipment, but it's middle of the road... not powerful enough to really be a supercomputer like some of the SGI, IBM, and HP gear, but is also overkill for just a database server. Sun has been moving to Opteron, so they may have a future in lower end systems. Time will tell.